Marine sediments are alive with all manner of creatures, including representatives of many lineages that are found nowhere else, such as this Kinorhynch, Echinoderes kristenseni (Ross Piper)

Well, it’s not much of a dragon, but it does live in mud. These animals, correctly known as Kinorhynchs, are miniscule, usually much less than a millimetre long, but under the gaze of a microscope they are quite appealing little things.

The specimen posing in the photo below was found in a kelp holdfast taken from the rocky shore in southwest Wales. These micro-habitats are seething with animal life, but you could say this about just anywhere in the ocean where there are sediments. The animals that live on and between these sediment grains are known as meiofauna and they’re bewilderingly diverse. It is in these marine sediments where you find the most animal phyla, many of which are found nowhere else, e.g. the Kinorhyncha.

All you need to do to see the incredible diversity of animals in these habitats is to take a handful of marine mud or sand and shake it with water for a bit. Then, let the sediment settle and all the animals will be swirling around in the water. Finally, pour the water through a very fine filter and observe the miniature menagerie with a microscope.

What we know about the Kinorhyncha and the other interstitial creatures could be written on their tiny undersides. For the most part they live out their lives out of sight and out of mind, but I’d quite happily wager that the finer details of what they get up to in the sediment is as fascinating as their appearance.

Just take a look at the photo below. This species, Crataerina hirundinis, takes liberties with house martins. The specimen in question was found on a young house martin that had fallen from its nest. Not only do they have something of the night about them, but these flies which have forsaken flight, scuttle about in a manner and at a speed, which makes you squeal like a girl. If you’re ever in the unfortunate position of having one of these on your person you’ll see what I mean. One moment it’ll be on your hand and the next it will have scampered, quite crab-like, to your armpit to seek refuge amongst the warm tangle of hair. One of these varmints in the trousers is not worth thinking about, but I’m sure some enterprising soul back in the middle ages probably devised some sort of torture device consisting of a handful of louse flies and a pair of metal trousers.

Louse flies, like this Crataerina hirundinis, are repulsive and fascinating in equal measure. This unlucky individual was found clinging to the body of a young house martin that had tried unsuccessfully to fledge the nest (Ross Piper)

Repugnant appearance aside they’re actually beautifully honed to a parasitic way of life. The body is flattened and the wings have all but disappeared so they can crawl about with ease in the bird’s pelage. The feet are like grappling hooks,  giving the insect a tenacious grip. With all these adaptations they scuttle around the body of the host with impunity searching for a good place to suck blood from after piercing the skin with the stylet-like mouthparts.

These elaborate feet give the louse fly a fierce grip (Ross Piper)

What I find most disturbing about these flies is their size in relation to the host. I suppose it would be something like a human playing host to a parasite the size of an edible crab.

The primitive state in all insects is two pairs of wings, each of which are essentially offshoots of the thoracic segments. Many of the more ancient insect taxa retain these two, almost identical pairs of wings (just imagine a dragonfly or a damselfly), while the more derived insects, such as flies, have tinkered with this original set-up so that the hind-wings have evolved into tiny, yet important vestiges known as halteres. In the beetles the fore-wings have evolved into very tough wing cases (eltyra), which protect the animal’s abdomen and its membranous hind-wings. In some of the beetles and the Strepsiptera it is the fore-wings that have evolved into haltere-like structures in a excellent example of evolutionary convergence. Some insects, e,g. certain stick insects have adapted to niches where there’s no need for wings and they have almost completely lost them.

Here's a Spanish robberfly roosting for the night on a flower head. The fore-wings are folded along the back, and the vestige of the right hind-wing, one of the halteres, is clearly visible as a yellow, stalked knob at the back of thorax. The halteres act like tiny gyroscopes and they are one reason why flies are among the most accomplished flying insects (Ross Piper)

Beetles still have two pairs of wings, but their first pair have evolved into protective cases, the elytra, while the hind-wings are membanous and can still be used for flight. The elytra protect the hind-wings and the abdomen. The majority of beetles can fly, although some of the larger species, such as this metallic green chafer from Trinidad are not the most graceful animal in the air (Ross Piper).

The Strepsiptera have to be among the weirdest of all the insects. This is a male Strepsiptera from Trinidad (not sure which genus, since the antennae are broken). In these insects it is the male's fore-wings that have evolved into halteres, while the hind-wings are used to propel the animal through the air (Ross Piper)

The huge variety of wing forms we see in the insects today had a starting point, but what was it? What structures did they evolve from hundreds of millions of years ago? Did they start off as as moveable bits of cuticle that helped terrestrial insects regulate their body temperature or did they evolve from the gills of juvenile aquatic insects? No one will ever know for sure, but some living insects give us a tantalizing glimpse of the possible origins of these structures. The nymph of a humble mayfly is one such creature.

On each of its abdominal segments the mayfly nymph has a pair of gills, each of which is equipped with a network of tiny channels much like the veins of insect wings. They’re also vibrated continuously by their own muscles to increase water flow around them thus improving gas exchange.

The mayflies are amongst the most ancient of all the insects. As juveniles, like the one in this photo, they have a pair of tracheal gills on each of their abdominal segments. Similar gills on the thorax of an ancient insect may represent the origin of the modern insect wing. In mayflies the winglets that will become the fully developed wings of the short-lived adult can clearly be seen extending from the thorax and covering the front part of the abdomen. This mayfly nymph is beautifully adapted for a life in fast flowing streams. Its hydrodynamic shape and strong legs keep a tenacious grip on slippery stones in the powerful current (Ross Piper).

It’s not hard to imagine the nymph of an ancient aquatic insect breaching the surface of a forest pool on the cusp of becoming an adult. As it shed its skin to begin its fleeting life as a terrestrial animal a mutation meant that the gills on each side of its thorax were retained. These ‘winglets’ let it scoot around a little better than others of its kind; even making short glides possible. With the passage of time and countless generations, evolution honed these gills into perfect wings that made true flight possible for the first time.

As seemingly risky as this way of life it has some huge benefits. Crucially, it allows two lives for the price of one and a division of labour. The larval stage is an eating machine and so all it needs are the structures to do this and do it well, i.e. well developed mouthparts and a metabolism tuned to efficiently turn this food into body mass.  The adult on the other hand can concentrate on the problem of finding a mate and continuing the life-cycle. The larvae has done all the growing, so apart from requiring fuel for scuttling around and flying the adult doesn’t really need to spend too much time with its face buried in food. With these two distinct stages the youngsters and the adults will never be competing with one another for places to live and things to eat, which means that any given habitat can support more of them.

As if developing through all these stages wasn’t enough, many insects have heaped another layer of complexity on top in a process known as hypermetamorphosis. The larvae that hatches from the egg of one of these insects isn’t a sluggish grub-like creature, but  a slender-limbed, extremely active beast, known as a triungulin, which scampers about looking for its host. The host depends on the insect in question that employs this strategy. Meloidea beetles, such as oil beetles, blister beetles, etc. are the most well known insects that go through hypermetamorphosis and these parasitise various solitary bees. The triungulins clamber onto the bee when its lapping up nectar from a flower and are taken back to its nest. If they’re lucky the mother bee will visit one of the nectar-filled brood cells in to which she has already laid an egg. One of the passengers will clamber on to this egg and use it as a raft before eating it and metamorphosing into a more typical, grub-like larvae. These chunky creatures can writhe around in the nectar and gorge themselves on it. The fat beetle grubs take on various shapes during their time in the bee’s nest and they eventually pupate to take on their bizarre adult form.

Beetles in the family Meloidea go through hypermetamorphosis and have larvae for different purposes. 1 is the triungulin, the active larvae that has to clamber aboard a host and get back to its nest. The triungulin turns into fat grub 2, which in turn becomes fat grub 3. 4 is the adult beetle, a female Meloe violaceus in this case (Harde - Blitz Edfitions & Ross Piper)

The photo below shows an interesting European Meloid (Cerocoma schaefferi), loads of which were found on flowers in an old quarry in northern Spain. Like all of their kind they also go have a triungulin stage, but instead of solitary bees, solitary wasps are what they seek. The wasps in question (Tachytes sp.) are specialist predators of mantids and grasshoppers and their kin. The wasps hunt and provision their nests with these insects and it is these the Cerocoma larvae eat.

These dazzlingly metallic Cerocoma schaefferi. beetles are in the act of laying the foundations for continuing their complex life cycle. This cycle depends on predatory wasps, their nests and the prey they stock these nests with (Ross Piper)

A blister beetle (Meloidea) from the rainforests of Borneo. Very little is known about the ecology of these tropical species.

The poor victim in the photo below was found in northern Spain and it was infested with no less than nine of these free-loaders. Just what harm they cause their host is unknown, but they can’t be doing it a world of good. A lot of mites are only parasitic when they’re young, forsaking this lifestyle for free, clean living as predators amongst the leaf litter when they reach adulthood. For the harvestman below this can’t come soon enough.

The amusing body-plan of a harvestman means that parasites on the bases of its legs are just about impossible to get rid of (Ross Piper)

Take a look at the photo below. This has to be one of the most convincing mimics. Just look at the shape of the head, the way the body is constricted in the right places to give an impression of a distinct head, thorax and abdomen and how the legs are held. It even goes to the trouble of pretending it has antennae by holding its fore-legs aloft. I think this is about as perfect as a mimic can get without becoming a body snatcher.

The individual in the photo is a female and it’s preparing its egg cocoon.

Master of mimicry. An ant-mimic sac spider (Sphecotypus cf niger, Corinnidae), female preparing her cocoon Bigal River Forest Reserve, near Sumaco NP, Ecuador. Image and identification courtesy of Arthur Anker. See more of Arthur's photos on Flickr under the username artour_a

The pair in the photos below were doing what insects do best on a poplar in the middle of Bishop’s Stortford. Once they’ve mated the female trundles up to the top of the poplar and the rest is a bit of a mystery since the larvae develop at the very bottom of the poplar just below the bark. This was the first time I’ve seen this fantastic insect after a tip-off from a local moth meddler.

If you’re out and about in the next week have a good look at any poplars where one side is exposed to the sun. The adults must be pretty short lived and during the couple of weeks when they emerge you may be lucky enough to see an adult or two low down on the poplar trunk. The best time to look for adults is between 7 and 10 in the morning when the females emerge and emit pheromones to attract a mate. The female’s chunky abdomen must make flying almost impossible hence the need to sit quietly on a tree trunk and attract a mate.

Even if there are no adults, host trees are riddled with holes at ground level and you can sometimes see the remnants of pupal cases poking from these holes.

Hornets or moths?

In the flesh the mimicry of these moths is incredible. Look at the fake eyes above the real eyes. These exotic-looking insects are probably more common than we realise.

Fortunately for the termite colony, the altruism of the soldiers knows no bounds. Occupying some of the soldier termite’s thorax and much of its abdomen is a large frontal gland containing a yellowish gunk. The walls of this gland are very thin and when the termite has repelled the invaders as much as it can with its mandibles it uses it mandibular muscles to burst itself letting the goo from the frontal gland ooze out. This gloop becomes very tacky on contact with the air and the attacking ants get hopelessly entangled.

Needless to say, the split in the soldier termite’s little body is severe and fatal, but in throwing a seven and taking an ant or two with them they have helped save the colony. This is surely the zenith of altruistic behaviour.

Happier times - A Globitermes sulphureus soldier before it bursts itself in a altruistic adios (http://www.termiteweb.com/termite-pictures-globitermes-sulphureus/)

Further reading:

Prestwich, G. D. Defense mechanisms in termites. Annual Review of Entomology 29, (1984)

Deligne, J., Quennedey, A. & Blum, M. S. “The enemies and defense mechanisms of termites”. In Hermann, H. R. (ed.) Social Insects Vol. II,  New York, Academic Press, 1982, pp. 1-76201-232.

Bordereau, C., Robert, A., van Tuyen, V., and Peppuy, A. Suicidal defensive behavior by frontal gland dehiscence in Globitermes sulphureus Haviland soldiers (Isoptera). Insectes Sociaux 44, (1997) 289-297.

Scheffrahn, R. H., Kreck, J., Su, N. Y., Roisen, Y., Chase, J. A., and Mangold, J. R. Extreme Mandible alteration and cephalic phragmosis in a drywood termite soldier (Isoptera: Kalotermitidae: Cryptotermes) from Jamaica. Florida Entomologist 81, (1998) 238-240.

To secure such evasive prey the trap ant has evolved a devilishly cunning strategy. Beneath the branches of its host tree, worker ants construct small galleries riddled with holes. More intriguing still is the way they actually build these galleries. Using hairs stripped from the surface of their host tree to act as a sort of fibrous matting, saliva and a specially cultivated fungus as resin, the ants construct these peculiar structures.

These galleries have been known about for a long time, but it was wrongly assumed they were simply a refuge for the ants whilst they were away from the nest foraging for food. As it turns out the real purpose of these galleries is far more sinister. The worker ants amass in these galleries with their little heads just inside the holes, their powerful serrated jaws agape. Here they wait in ambush and before long a plump cricket ambles in to view exploring the branch tentatively with its long limbs and sensitive antennae.

Worker Allomerus decemarticulatus waiting to spring their trap (Alain Dejean)

The hairs that clothe the tree’s outer surface are a deterrent to walking insects. The smooth surface of the gallery on the other hand will seem like a fine place to rest or have a snack. Sensing nothing out of the ordinary about the ant gallery the cricket walks straight on to it. Two or three of its clawed feet may probe the holes for purchase and it is then the waiting ants strike. They grab the ends of the cricket’s legs and heave, pinning the cricket to the surface of the gallery. Other workers rush out and begin dragging the remaining limbs and antennae into the holes until the prey is well and truly snared. Other workers then swarm all over the prey and sting it. With the prey immobilized and at death’s door the ants can begin their gory work. Using their powerful jaws they begin butchering the carcass of the cricket, chopping out chunks of flesh to carry back to their developing sisters in the nest pouches.

For this cricket, the leaf-munching party is over. It has fallen foul of the trap ant's cunning ploy and will soon be nothing more than ant-grub food (Alain Dejean)

This amazing trapping strategy ensures the ant larvae have a good supply of protein in an arboreal environment that it otherwise lacking in nitrogen containing food fit for ants. Not only have these ants evolved a unique way of catching animals much larger than an individual in the colony, but the whole set up is the product of a symbiotic relationship between the ant, its host tree (Hirtella physophora) and the fungus. The ant has a safe place to nest in the leaf pouches of the tree. A favor repaid by ridding the tree of herbivorous insects that can’t wait to get stuck into the succulent leaves of the Hirtella tree. The fungus used as an adhesive in the construction of the trap galleries is thus cultivated by the ants and is spread to areas where it might not reach under its own steam.

Further reading:

Dejean, A., Pascal, J. S., Ayroles, J., Corbara, B., and Orivel, J. Arboreal ants build traps to capture prey. Nature 434, (2005) 973.

In most cases, a female parasitoid wasp deposits her eggs on or in the host, but this is far too pedestrian and safe for the trigonalids. These mavericks of the wasp world like to make things more difficult for themselves so the female deposits her eggs on plant leaves. If this were the end of the story these wasps would not have lasted very long. No, the egg-in-the-leaf-trick is merely a ruse. The female trigonalid uses her short ovipositor and the unique structure of her abdomen to punch out a small piece of tissue from near the margin of a leaf, replacing it with a flattened egg. She deposits a few eggs in one leaf before moving onto another leaf perhaps on a nearby plant. This goes on until she gets eaten or exhausts her eggs, which in some species of trigonalid can be as many as 10000 – a huge number for a parasitoid, which underlines just how haphazard this strategy is.

The whole purpose of going through the laborious act of laying thousands of eggs in leaves is so that her offspring can get swallowed by a caterpillar or the larva of a sawfly. If the very tough egg is lucky enough to get swallowed it hatches which is thought to be triggered by the physical action of being chewed and/or salivary secretions. For most parasitoids, getting into a plump caterpillar would be mission completed and cause for celebration, but no such luck for the tiny trigonalid larva. The tiny larva winds up in the caterpillar’s gut and wastes no time in breaking out of there to gain entry to the haemocoel, the insect body cavity that is bathed in haemolymph. The trigonalid makes its way through this liquid searching for its real quarry – another parasitoid that has already infected the caterpillar. Lots of parasitoids, such as other wasps and flies, are dependent on the larvae of lepidoptera and sawflies and it is these the trigonalid larva is after. If it’s lucky it will find its prey, attack them and eat them, but in many cases the trigonalid that has defied the odds to get swallowed by a caterpillar will find nothing suitable to predate once inside or the only parasitoid within the caterpillar will be too large for the trigonalid to tackle. In both cases the poor little trigonalid is doomed. However, some species of trigonalid are able to sit tight inside the caterpillar until its gets parasitized by an ichneumon or a tachinid fly. There are a couple of drawings of trigonalid larvae below.

This isn’t the only bizarre life-cycle of the trigonalids. Another strategy used by some species also hinges heavily on coincidence, but the supporting cast is slightly different. These species still depend on a caterpillar or sawfly larva, but this time the caterpillar must be captured by a vespid or eumenid wasp, butchered and fed to one of the wasp’s grubs back at the nest. In the flesh of the dead caterpillar are the eggs of the trigonalid and once swallowed they hatch to feed on the unfortunate wasp larva.

In the world of wasps, trigonalids are something of an enigma. Only around 100 species are known, the adults don’t live very long and their precarious way of life means they are rather rare, so we don’t know a great deal about them. Their geographic distribution, appearance and lifestyle suggest they are very ancient and some entomologists have theorized they may be something of a missing link between the sawflies and the rest of the hymenoptera (the apocrita). Indeed, the oldest trigonalids are known from 100 million year old lumps of Cretaceous amber, which shows this way of life, precarious as it may be, has been going on for some time.

Trigonalys sp. (female). A species from the Central African Republic. These wasps have quite a distinctive appearance. Note the unusual shape of the abdomen that enables the female to press out a small piece of leaf tissue (Simon van Noort - www.waspweb.org).

Trigonalys natalensis (female). A species from Tanzania. The unusual structure of the abdomen is less pronounced in this species (Simon van Noort - www.waspweb.org).

Like all insect larvae, immature trigonalids are unsightly to say the least. On the left we have a third instar larva of Bareogonalos jezoensis from Japan. This instar has huge mandibles for making short work of the prey. On the right is the final instar of the same species. The big mandibles have gone and instead we have a chubby beast with a tiny head. This species is a parasitoid of vespid wasps (Seike Yamane, 1973).

Further reading

There’s more about these wasps in the book, Extraordinary Animals

Weinsten, P. & Austin, A.D. 1991. The host relationships of trigonalyid wasps (Hymenoptera: Trigonalyidae), with a review of their biology and catalogue to world species. Journal of Natural History 25, 399-433.

Yamane, S, 1973, Descriptions of the second to final instar larvae of Bareogonalos jezoensis with some notes on its biology (Hymenoptera: Trigonalidae), Japanese Journal of Entomology (Kontyu), 41, 194-202.