Our Window on Nature

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Insect Architecture

Filed under: Bugs — Lowell Christie -- August 27, 2014 @ 6:41 pm

Think small. We’ve observed many insect architects lately and have been astounded by their diligence. Many of them slave away in campgrounds and in parking lots, oblivious to lazy humans who idle in the shade while they watch others work.

Most insect architects belong to the order Hymenoptera (which includes bees, ants, and wasps), but there are significant exceptions. For example, the praying mantis (a fairly primitive insect), is related to the cockroach, and ant lions are related to lacewings and dobsonflies.

Their reasons for building are as diverse as the insects themselves. Bees and wasps build elaborate nurseries for their young; moths spin cocoons for protection during pupation; ant lions dig pitfall traps to capture game; and caddis larvae build houses that they can add on to as they grow. These latter two insects will be examined in this article.

Trapping prey isn’t a common method of obtaining food in the insect world. These animals first must possess the skill necessary to build the trap, and then they must exercise the patience to wait for dinner to arrive. Such an insect is the ant lion.

Ant lions are found throughout much of the country, wherever there is suitably sandy soil in well protected locations. You may have seen their tiny pits under a ledge or at the base of a bush. In many parts of the country these insects are called doodle bugs, but a friend claims that in her neighborhood, all the kids called them “dooey-dooeys,” though why she couldn’t say. All this insect has in the way of tools is a pair of long mandibles (jawbones) and very strong neck muscles.

The ant lion backs around and around in a tight circle (it can move only in reverse gear) tossing away grains of sand and small pebbles as it moves. A hole forms, gradually becoming deeper as the industrious little creature throws out more and more grit, until several hours later, when the ant lion finds itself at the bottom of a steep-sided, cone-shaped pit.

Having worked up a considerable appetite, no doubt, the ant lion waits at the bottom of the pit with all but its mandibles hidden beneath the sand. When an ant or other crawling insect ventures over the lip of the pit, it starts a landslide, and then, in the time-honored one-step-forward, two-steps-back tradition, it slides toward the hungry ant lion. The ant lion isn’t casually waiting below. As soon as it perceives the struggle of its prey, it starts tossing up sand to hurry the ant’s downfall.

As soon as the ant is within range, the lion grabs it, injects a dissolving enzyme, and waits for the enzyme to do its work. The enzyme liquefies the soft parts of the insect, so that the ant lion can suck out the nutrients through its mandibles (at this stage the mandibles act as straws). Dinner over, the ant lion tosses out the carcass, repairs its pit, and settles down to await the next meal.

The architecture of caddis insects has an entirely different purpose from that of the ant lion. As the largest group of aquatic insects, caddis are found in nearly every part of the world – in swift-running streams, in quiet lakes and ponds, and even in swimming pools that have accumulated plant detritus during the winter. The United States is home to several hundred different species. Fishermen who know their value as bait are likely to call these insects caddis flies, but entomologists point out that caddis belong to an entirely different order from flies. In fact, adult caddis resemble moths more closely than flies, except that the caddis have hairy – as opposed to scaly – wings.

Unlike the adults, caddis larvae live under water, and it is they who go into the construction business. Soon after hatching, a tiny caddis larva builds itself a “house” to provide protection from fish and from larger insects with an appetite for fresh caddis. Naturally, the larva has to keep adding to its case as it grows.

Each species of caddis has its own particular style of architecture. Some use pieces of leaves, grass, or twigs to build their homes. One species of “stick-case” builders constructs its tube from plant fragments that are cemented in a decorative spiral. A “log-cabin” builder stacks pieces of plant material crosswise, as though it were building a tiny log cabin. From the outside the case appears square, but the insect inside chews into the side of the “log” closest to its body so that the interior space is perfectly round. That makes it more comfy, no doubt.

Many species of caddis use sand or gravel as building material. By constructing its case of grains of sand from the bottom of the stream, the caddis is perfectly camouflaged as it slowly creeps about to feed. It wouldn’t be fair to credit the caddis with an artistic sense, but members of this species do use decorative objects on their cases at times. If there are tiny snail shells available, they may be added to the case. If one of the shells should happen to be occupied, too bad. In gold country, caddis hunters sometimes find tiny gold nuggets cemented into the cases, and in areas where water-worn glass is available, there may be fragments of red, green, or brown.

Once the caddis is ready to pupate, it attaches its case to a twig or rock and seals up the door where, safe from predation, it makes the transition into an adult. Then, freed from the aquatic world and nearly able to fly, the adult emerges and wiggles to the surface, leaving its empty case behind.


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