Last year at about this time we were wondering what a cold winter would do to some of the common insect pests--unfortunately, it didn't do much! Now, some may be wondering what a warm winter will mean to insect populations. Climate usually has some impact on insect populations; it may not be a great impact, but there may be something noticable in some insects and other animals. In general, insects are more dependent on temperature (an average daily temperature) than availability of food. Long periods of warmer-than-usual weather in the winter may provide some species the chance to survive the winter in larger numbers, and perhaps get a jump-start on spring.
Many insects hibernate (in a sense) during the winter, while others simply become inactive because it is cold. Mild to warm weather (temperatures here the last few weeks have been in the 60s!) may initiate breeding of insects such as mosquitoes, cluster flies, boxelder bugs, and others. Hopefully, the natural parasites and predators of these insects will become active at the same time. Warm weather may give some insects the opportunity to have more generations this year than usual; more generation may mean more of these critters available during summer. Of course, some insects have just one generation per year; so, for them there is little advantage to this weather.Some groups that may benefit from a mild winter include:
Aphids and Scale Insects - These insects usually overwinter as eggs. They hatch in the spring and remain on one host or have separate generation on two hosts. Warm weather may provide for more of the eggs to survive and an earlier flight time after hatching. Many insecticide applications for aphids and scale insects are timed for their "normal" flight period. Deviations in this could put the insecticide on the target site too early or too late! If the winter continues to be a mild one, it might be necessary to monitor aphid flight times, and when the crawler stage of scale insects appear, if control measures are taken.
Slugs - These creatures are often pests in flower and vegetable gardens in the spring--and there are few good measures to control them! (I don't like wasting good beer!). Most slugs and other snails overwinter in the egg stage and become active in early spring. A mild winter may get some of them started early, and feeding on plants that are also getting a boost by the warm and wet weather. Slug control may be a big challange in the spring of 1995!
Spiders. These are predators and they depend primarily on insects for their prey. Most spiders overwinter in the egg stage, but some as spiderlings. An increase in the activity and availability of flies, beetles, and other insects can provide for a large population of spiders if the spiderlings can find more food in early spring (oh, joy!). Daddy long-legs (not really spiders, but close enough) may get a good boost from a mild winter.
Mosquitoes. These flies usually overwinter as adults, and they are ready to go in the spring! They lay their eggs in standing water that results from melting snow and spring rains. The larvae complete their development in the water and adult mosquitoes are produced in a few short weeks. The warm and wet weather could provide some added problems in a few months. Homemakers should consider some early efforts to remove standing water around the house. The best control is to prevent the female from finding a place (standing water) to lay eggs, which the larvae need for survival.
Fleas. What, you are saying! Not fleas! Well, fleas are a problem in summer and fall primarily because of the relative humidity outdoors and indoors. Humid conditions outdoors (summer) usually leads to increased relative humidity indoors, and this may provide conditions suitable for flea populations to increase. If we have a humid and warm winter, fleas could become a problem, or at least get an early start in the spring! Effective flea control in the winter can be acheived with regular vacuuming of the pet's sleeping area. This will remove flea eggs and the dried blood (from feeding adult fleas) that can accumulate in the bed.
House Dust Mites/Allergies. Not unlike flea populations, house dust mites respond to indoor humidity. When the relative humidity indoors (and outdoors) is below about 50%, house dust mite populations decline. During the winter, allergic reactions to these arthropods usually decreases--some small blessing from winter. However, a wet and warm winter may provide conditions for these mites to increase above normal winter numbers. We are learning that about 17% of the U.S. population are allergic to house dust mites and other arthropods (cockroaches) that live indoors. (Don't be alarmed, the percentage is thought to be about 30% in the northern European countries!) Winter vacuuming may not be a reasonable control strategy for dust mites; this activity may result in more allergen being introduced into the air than is being removed by the vacuum.
Carpenter and Yellow Ants. The colonies that are located within structures (houses, barns, garages, etc.) are inactive during the winter (due to a shortage of food), but often begin foraging in early spring (February)--and are seen indoors. Outdoor colonies that live in logs and trees are inactivated by the temperature (and a scarcity of food), and forage in April. Colonies may become active earlier in the spring if the winter temperatures are mild. If the winter continues in a mild state, be prepared for an increase in calls about these and other ants--especially yellow ants. These ants are very responsive to warm spring temperatures. The swarming of yellow ants is often confused with the swarming of termites. Yellow ants generally live under slabs, sidewalks and adjacent to house foundations. They do not infest indoors nor do they attack structural wood.
Termites. These wood-infesting insects are also very responsive to winter and spring temperatures. Swarming is usually in April and May, but it is very much linked to warm and wet weather. Certainly, warm weather in mid winter will not result in swarming (at least outdoors, but maybe indoors), but a continued mild winter could result in early swarm dates in some areas that traditionally have mild winters (tidewater region).
Clover Mites. These reddish brown mites are a common pest in turfgrass in the early spring. When they occur, usualy in recently established lawns, they may be in large numbers. They can cover the sides of houses and sometimes enter through windows and become an indoor pest. While they do little damage to turfgrass, they can be quite a nuisance--and quite unpredictable. Mild winter temperatures are often linked to large pest populations of these arthropods. But these mites are often numerous on a 3-year cycle in some areas.
Ticks. There is some evidence that mild winter temperaturs provide for increased tick populations the following spring and summer. This may be linked to their being able to locate a host (mouse) in the early spring. Rocky Mountain spotted fever and Lyme disease (carried by ticks) are known from Virginia; thus, increased tick activity can be a threat to those outdoors.
Gnats. These flies are perhaps the most common indicators of mild winter weather. On warm, sunny days with little wind, these flies can be seen in small swarms over the ground. They usually find some "marker"--a light colored or dark colored area that is distinct from the background, and over this area they will swarm for an hour or less. Warm spells in the winter will provide these flies more opportunity to swarm, more swarming means more mating, more mating means more eggs, and then more gnats! Ain't life grand!