JULY
1998

 

 

 

By
Tom Turpin
 
Professor of
Entomology
Purdue University

 

 

 

 

 

7-09-98

Rainy Days Bad for Hair and Bugs

An old joke asks: "What kind of leaf does a rabbit sit under during a rain?” The answer, of course, is "a wet one!” The same could be said of insects.

In general, insects are not well equipped to survive falling rain and the water that results. To be sure, many insects benefit from rain. Especially those that live in water. Some insects spend their entire life in or around water. The names of water bugs, water striders and back swimmers suggest that they are well adapted to deal with water.

Other insects develop as immatures in water. For instance, that summer-time scourge the mosquito is a water dweller as a larva. The same is true of dragonflies, mayflies and caddisflies. Larvae of other insects, such as horse flies and deer flies, live in nearly saturated soil. Immatures of fireflies, called glowworms, live in damp soil along creeks and in swamps.

Most insects need moisture in their habitat but could do without the rainstorms on the plains, or in the forests for that matter. Millions of insects die as a result of rain and wind.

Insects not adapted to living in saturated soil will drown if the soil is water-logged for an extended period. Some insects that form their pupal chamber in the soil actually will waterproof the chamber. That works to keep moisture in during dry periods and out when the soil is saturated.

Any insect that lives exposed on plants can be harmed by a downpour. Many insects literally are knocked off their food plant by hard rains. Many times the insect will become stuck in the mud and die. Some caterpillars, even if they are not killed when knocked off the plant, are unable to find their way back to a food plant and die of starvation.

Newly hatched and small and soft insects can be smashed by a drop of rain. Very young insects frequently drown in water trapped in leaf axiles of plants. This can be of benefit when the insect is a pest. For instance, when young corn borer larvae drown behind the leaves of corn, it may eliminate the need to chemically control the pest.

Wet weather also has an impact on adult butterflies and moths. These insects with large scaled wings don't fare well in thunderstorms. Wind and rain can knock scales from their wings; it can tear the structure as well.

Butterflies do the best they can to take cover when a rainstorm approaches. Generally, they hang upside down under a leaf or a stem. With their wings folded and hanging down, little surface is exposed to the elements.

Other insects use structures to gain refuge from storms. Many wasps build their nests in barns and garages or under eves for that reason. Some adult insects move into shelters during storms. That is why fly populations increase on porches and in homes prior to and during a rain.

While severe storms are a hazard for humans, any hard rain is a problem for insects. For most insects, a rainstorm is a life-and-death matter, not just a bad hair day!

 

Writer: Tom Turpin
Editor: Olivia Maddox