Topics in Insect Ecology

by Gary A. Dunn, M.S., F.R.E.S., Director of Education


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Where Do Insects Go in the Winter  [TOP OF PAGE]

It often looks like insects have totally disappeared from the winter landscape. Where have they gone? Well, in most cases they actually haven't gone anywhere. Despite the fact that insects are cold-blooded and rely on the temperature of their surroundings to keep them warm, insects have been successful in developing methods for surviving during the cold, winter months.

Many insects pass the winter in the egg stage. Insect eggs are ideally suited for withstanding the hardships of winter. The eggs have shells that are thick and water-tight. In many cases the eggs are covered with hairs, silk, or frothy materials produced by the female before she died. These provide an extra degree of protection by insulating the eggs.

Other insects enter into a special type of hibernation known as diapause. In these cases the insects go into a deep rest, thereby greatly reducing their bodies needs for energy. Entry into and awakening from diapause is generally controlled by daylength (the length of daylight hours) rather than environmental conditions such as temperature. This prevents insects from being "tricked" out of diapause in the middle of the winter by a period of warm weather (which is not uncommon in many parts of the country). Insects may hibernate in either an immature or adult stage. Obviously those insects that require more than one year to complete their development must pass at least one winter as an immature form (nymph, larva, or pupa). Some of these insects are soil dwellers or wood borers and are able to escape the cold conditions by digging deeper into the soil or wood. Insects that hibernate as pupae generally cover the pupa with a thick, insulating covering of silk and/or plant materials; this type of pupal covering is referred to as a cocoon.

For those insects that overwinter as adults, they must find a sheltered, protected location such as a hollow tree or log, leaf pile, animal nest, or the soil. Since these hibernating adults have already completed their growth and development they are almost always the first to appear in the early spring. This is why the mourning cloak butterfly, which is one of the few butterflies to overwinter as an adult, is the first butterfly to be seen in the early spring. Some insects such as ladybird beetles, cluster flies, boxelder bugs, leaf beetles, root weevils often use our homes as overwintering sites. However, despite the warm temperatures in these buildings, most insects still go into diapause and cease all activity until spring. In fact, they generally prefer to spend the winter in attics, walls, or crawl spaces where it is cool, but not cold.

A few insects migrate south for the winter and then reinvade the northern areas the following year. The best example of this is the monarch butterfly. Monarchs from all over North America migrate to either central Mexico (those butterflies from east of the Rocky Mountains) or southern California (those butterflies from west of the Rocky Mountains. In the spring the butterflies spread north again and reclaim their breeding grounds.

A few insects are active year round, or only active during the winter months. The immature stages of many aquatic insects are able to remain active throughout the year. The adults of the winter stoneflies are active only during the late winter and early spring months, and certain springtails (nicknamed "snow fleas") and winter scorpionflies are also active during the winter months. Most of these insects are equipped with special body fluids that act as antifreeze and prevent the insects from being harmed by the freezing temperatures.


Insects and Plant Galls  [TOP OF PAGE]

Galls are a common sight on many plants, including weeds, shrubs and trees. Galls are abnormal outgrowths of plant tissue produced when a plant attempts to recover from an injury caused by an insect or other organism (fungi, slime molds, bacteria, viruses, nematode worms, or mites). The insects and mites are the most common causes of plant galls. Insects responsible for gall formation include gall wasps, gall flies and midges, aphids, caterpillars, beetles and thrips.

Insect galls are the result of potent growth stimulating substances that are secreted by the insect (egg-laying adult or developing immature). Many insects live inside of developing galls. These galls usually consist of two distinct layers - an outer protective layer and an inner nutritive layer. Through the process of evolutionary trial and error gall insects now feed at the proper rate so that they do not kill all of the developing plant tissue. Thus the gall insect benefits by obtaining reliable food and shelter, while the plant is neither harmed or benefited.

There are many types of plant galls and each insect produces a totally unique, characteristically-shaped gall. The variable physical appearance of the many galls is due to the type of insect causing the gall and the part of the plant affected. Galls may occur on just about any part of a plant - roots, stems, twigs and branches, leaf stems, leaves, buds and flowers. Some galls have commercial value. They are used in the manufacture of inks, dyes, tannic acid, medications and food.


Protective Coloration in Insects  [TOP OF PAGE]

Insects are not always able to defend themselves, and so many of them have developed ways for blending into their surroundings. Some insects hide in plain sight, their bodies resembling non- living or inedible objects such as bark, thorns, buds, twigs, leaves, or bird droppings. That's right, the caterpillar of the viceroy butterfly looks just like a bird dropping and easily gets passed up by an animal looking for a meal. Other insects, such as the stick insects are shaped like twigs or leaves. The dead-leaf butterfly of India is also another example of this type of protective coloration and camouflage. When they fold their wings over the back, the undersides of the wings look just like dead leaves - complete with stem, leaf veins, and shiny spots that look like holes nibbled by leaf-feeding insects. Many night-flying moths are colored and marked so that they "disappear" when they sit on a rock or tree trunk during the daylight hours. Some insects create a disguise for themselves by covering their bodies with plant parts, stones, dirt, cast skins, and other inedible "junk".

Insects may have another reason to use camouflage: to improve their chances for sneaking up on their prey. For example, some mantids are shaped and/or colored like flower petals or leaves and go unnoticed by plant-inhabiting insects.

Some insects are brightly colored and can't help but be noticed by other animals. These insects are also using their coloration as protection, but in a very different way. Some insects (such as orange-and-black monarch butterflies and milkweed bugs and red-and-black ladybird beetles and milkweed beetles) are using their bright colors to warn other animals that they are distasteful and should not be eaten. Other insects (such as black-and-yellow bees and wasps) are telling other animals to stay away because they can defend themselves by stinging.

From camouflage to warning colors, it's all a type of protective coloration and insects make effective use of it.


Ants and Aphids  [TOP OF PAGE]

Throughout the ages, humankind has had its share of dynamic duos -- Adam and Eve, Samson and Dililah, Anthony and Cleopatra, Bonnie and Clyde, Rogers and Hammerstein, and Batman and Robin, to name a few. Insects also have their duos. Ants and aphids are often found together. Both gardeners and homeowners know that either of these insects can sometimes be pests, but when they show up together it can only mean double trouble.

Aphids, sometimes called plant lice or greenbugs, and ants have a special relationship where they help each other. Aphids provide a food resource for the ants and ants provide protection for the aphids. Some people think of the ants as "farmers" and the "aphids" as cows.

Ants feed on the honeydew produced by aphids. Aphids feed on the sap of plants, filtering out the nutrition they need and eliminating the rest. This sticky liquid, known as honeydew, includes a high concentration of sugar and is highly prized by ants. It is the sticky honeydew that sometimes gums up cars parked under aphid-infested trees. The sugary honeydew also provides an excellent place for fungi to grow. Sooty mold growing on aphid honeydew often turns aphid-infested plants black.

Since the ants are harvesting the honeydew produced by the aphids, they become quite possessive of their "cows". The ants protect the aphids from predators, like ladybird beetles and lacewings, and parasites. Ants even carry aphids to uninfested plants to provide fresh "pastures" for their herd.


Most of this information is reprinted from Insect World, one of the two periodical publications produced by the Young Entomologists' Society. Information on Insect World (or Y.E.S. Quarterly).  Click here for enrollment and subscription information.


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