Nick Baker’s hidden Britain
Ant woodlouse
Ants are just about everywhere on land. They dominate so many habitats – including our lawns, allotments, patios and pavements – that they represent a valuable resource to any animal able to outwit their impressive array of defences and infiltrate their citadels. Of the ant-loving, or myrmecophilous, species that develop complex relationships with these supersocial insects, arguably none is more beautiful nor more furtive than the diminutive Platyarthrus hoffmannseggii or ant woodlouse.
You might think this creature would be difficult to find, given it is 5mm long and rarely found outside ant nests. However, flip over a flat, sun-warmed object such as a rock, paving slab or piece of corrugated iron (anything that acts as a natural solar panel and storage heater) and you’ll often see one hunkered down among the ant brood. Its blanched white complexion contrasts with the dark soil and ants, yet it’s unmistakably a woodlouse, just smaller and paler than you might be used to.
Being a woodlouse, it feeds on pretty much anything it can scavenge, including ant droppings, dead ants and the husks of the ants’ insect prey. The ant woodlouse will also steal ‘trophallactic’ pellets – that is, food shared between ants via regurgitation. Close and careful observation in a captive situation sometimes reveals the woodlouse ‘begging’ for this food source by facing an ant and stimulating it with its antennae. As far as the ants are concerned, this inquiline (an animal that occupies the living space of another) may provide a sanitary service. By acting like some 14-legged chambermaid, it is likely to help keep the ants’ tunnels and galleries clean. Undoubtedly part of the fascination is how it gets away with it. Any other woodlouse would be at best harried, or at worst quickly attacked, overcome and dismembered as food. But dainty little hoffmanseggii seems to be able to go about its business without any of this hassle and risk. It’s almost as if it is accepted as an ant itself.
The theory goes that an ant woodlouse can infiltrate the host colony by taking on the odour of the ants, and acquiring the scent ‘badge’ unique to each
colony. This enables it to bumble around with confidence, dodging between the ants’ legs and pretty much going where it pleases, even being treated like a fellow colony member.
If an ant woodlouse is transferred to a different colony, however, it behaves and is treated very differently. For a start, it runs more – and it’s fast, too. This initial response to disturbance is often seen when you expose one of these animals by turning over its hiding place. The woodlouse dashes away to hide, with its flattened antennae quivering. Should speed fail, the ants will harangue it aggressively. Now you get to see how that broad carapace comes into its own, complete with flattened epimera (the flanges that stick out to the side, giving a serrated appearance).
When attacked, an ant woodlouse hunkers down, tucks in its antennae and becomes immune to the ants’ collective efforts. If the attack continues, the woodlouse will raise the two strange pointed organs on its rear, known as uropods, from which a liquid is excreted. This has a repellent effect and turns to a sticky goo, effectively gumming up an ant’s mandibles.
NICK BAKER is a naturalist, author and TV presenter.