Detachable Bristles Immobilize Ants

close up of millipede with white bristles on a orange background

Biological Strategy

Polyxenid millipede

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Attach Permanently

A living system can conserve energy by attaching permanently to a particular site because it can take advantage of resources that come its way, rather than expending energy to move to resources. A permanent attachment, intended to last the lifetime of the living system, creates special challenges. For example, physical mechanisms, such as the anchor that holds a marine algae to the ocean’s bottom, must be able to withstand forces that can pull it off its substrate. Chemical mechanisms, such as a barnacle’s glue, must avoid both physical and chemical breakdown, such as being dissolved by water.

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Capture, Absorb, or Filter Organisms

Many living systems must secure organisms for food. But just as one living system must capture its prey to survive, its prey must escape to survive. This results in capture and avoidance strategies that include trickery, speed, poisons, constructed traps, and more. For example, a carnivorous plant called the pitcher plant has leaves formed into a tube that collect water. Long, slippery hairs within the tube face downward. When insects enter the tube seeking nectar, they lose their footing and slide inside, unable to climb out and escape being eaten and digested by the plant.

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Protect From Animals

Animals–organisms that range from microscopic to larger than a bus–embody a wide variety of harms to living systems, including other animals. They threaten through predation, herbivory, defense, and parasitism, and they compete for resources such as water, nutrients, and space. Any given living organism commonly faces threats from a variety of animals, requiring strategies that effectively defend from each. Trout and other bony fish, for example, escape predators by having scales made of very thin, flake-like pieces of bone covered with slippery mucus. They also have behavioral strategies such as camouflage, fast swimming, and twisting and turning to achieve release from a predator’s grip.

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Myriapods

Class Myriapoda (“many feet”): Centipedes and millipedes

The species in this class are defined by their feet. The name centipede means “one hundred feet” and millipede means “one thousand feet”. Although myriapods don’t have exactly 100 or 1000 legs, centipedes have one pair of legs per body segment while millipedes have two pairs per segment. Centipedes have a flattened body and are fast-moving carnivores who use venom to kill their prey. Millipedes, on the other hand, are rounder in shape and move slowly through soil to eat decaying plants. Both animals like to live in dark, moist environments that allow them to stay protected and hydrated.

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Caudal tufts of bristles on the Polyxenid millipede immobilize predators (ants) because the detachable bristles have grappling hooks on the end and barbs along the shaft that promote entangling.

“Unlike most millipedes, whose body surface is smooth, P. fasciculatus is densely beset with bristles. These are neatly arranged in transverse rows along the back, and in sets of flower-like clusters along the flanks. Projecting from the rear and glistening conspicuously in the light was a tuft of bristles much finer than those on the body. There appeared to be something special about that tuft, in that the animal seemed to make use of it when provoked…the polyxenid’s caudal tuft is really a pair of tufts, which the animal usually holds closely appressed. The tufts’ bristles are slender, and consist individually of a shaft densely beset with barbs and a tip fashioned as a grappling hook. The bristles are loosely anchored. Give them the slightest tug and they detach.”

The authors then exposed ants to the millipedes and watched as the millipede swiped the tufts on the ants. The grappling hooks fastened to the ants’ hairs and thoroughly entangled them.

“The bristle tips are the functional units that ensure that the bristles become anchored to the ant. As grappling hooks they become fastened to the hairs (setae) that project from the ant’s surface, with the result that the bristles are then torn from the tufts. Also of importance are the barbs that project from the bristle shafts, for these act as hooks by which the bristles become cross-linked. Fastened to one another, the detached bristles form a loose meshwork by which the ant is muzzled and its legs are strung together. The ant is literally tied up.” (Eisner 2003:106-107)

Last Updated August 18, 2016

References

Book

For Love of Insects

31/10/2005 | Thomas Eisner

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