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Because of their small size and brief lives, insects are very much at the mercy of the weather. Many species have adapted to cope with these difficulties in countries where the weather is unpredictable and no two years are alike.

Most plants and animals of temperate regions are regulated by their environment and the weather. The effect of weather on insects may be direct or indirect, such as affecting their food plants or their chance to mate, but the results can be very noticeable, leading to good or bad seasons in different species.

More remains to be discovered about the effect of weather on insects, but research has revealed some interesting facts. Here we examine some of the day-to-day effects of the weather on insects.

The geographical position of many countries gives them an everchanging and unpredictable weather pattern. Still, with small cold-blooded creatures like insects, the day-to-day weather has its most significant impact.


How The Sun Affects Insects

Air temperatures and sunshine are the most important features of weather for insects. Like all life forms, insects function better at higher temperatures, and many need to raise their body temperatures. Temperatures of insects need to be about 200-300 C (68 0-860 F) before they can move around and fly freely.

Most insects are inactive on cold, dull days, resting on vegetation or hiding away. However, a cold, sunny day benefits those insects that bask in the sun. A sunny day in early spring will bring out clusters of ladybirds.

Like many other insects, these beetles use sunshine to warm up sufficiently so they can crawl about and feed. By basking, they can speed up the transition from their reduced winter metabolism to the frantic physiological activity of reproduction.

Many Butterflies also take advantage of the early spring days to seek a mate. However, if the spring is cool, dull, or wet, many species do not get the start they need, which can also be detrimental to their numbers the following year.

On hot sunny days, insects can balance their body temperature at a level preferred by the particular species. The marsh fritillary caterpillar has a preferred body temperature of 35 C (95 F) when basking, but the speckled wood adult tries to maintain its body temperature at a much lower 28 0 C (82 F).

A garden at the height of summer hums with insect activity on such warm sunny days. Day-flying insects make the most of this sunshine, packing as much as possible into these few days. Many short-lived insects must mate and reproduce in these few warm days.

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Weather Affects Future Generations

We usually assess how successful and widespread an insect species is by measuring whether it is common or rare in a particular year. However, weather affects all stages of insect life history, subtly influencing their success in reaching adulthood.

For most insects, the most important and vulnerable stage of an insect’s life is when it is an egg. The number of eggs laid directly influences the number of adults in the following generation.

Several populations of butterfly species have been studied in detail, and the failure of females to lay all their eggs is one of the significant factors influencing numbers.

Most female orange tips, meadow browns, wood whites, and marsh fritillaries die before laying more than about half of their total egg load.

The primary reason for this is that the females do not have the opportunity to lay all their eggs because of changing weather conditions.

Even before egg-laying can begin, the insects have to mate. For this to occur, both partners must be fully active, which only happens in warmth and sunshine. A good time to look for insects is on a sunny day after a week of dull, cool weather, as large numbers of mating insects can be seen.

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How Weather Affects Egg Laying

Once mating has finished, the female must choose a suitable site for her eggs. This is an energy-consuming process, so she needs to be fully active.

The characteristic patchiness of weather usually means that female butterflies can lay their eggs during a small fraction of the daylight hours.

One way around this problem is to lay several batches instead of individual eggs, thus reducing the time spent searching. Such a practice is especially apparent among insects that lay their eggs in early spring.             

Cold weather may also influence the pattern of egg distribution. In warm years the brown hairstreak butterfly lays her eggs individually on hawthorn twigs. In years of poor weather at breeding time, the eggs have been found clustered together or laid in pairs. Females do not typically fly in dull weather, so they crawl up and down the twigs to lay their eggs.         

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How Weather Affects Larval And Pupal Stages

Weather conditions may also interfere during an insect’s larval and pupal stages. In early spring, the winter moth is affected by temperature, and a cooler period can extend the time spent as larvae or pupae. This does mean that the larvae and pupae are about for longer, so they are more likely to be found by birds and eaten.

In spring, the caterpillars of the winter moth hatch. They hatch high up in oak trees before spinning a strand of silk that they use to float to neighboring trees and bushes.

Winter moth caterpillars feed on bursting leaf buds, so they must reach their food in time. Because all trees have their own time of leaf growth, the weather affects whether the caterpillars will reach the plant in time to feed on the leaves.

Photo of bee

Insects That Arent Affected

Some insects aren’t affected as much as others by the weather. Social bees and wasps can control the environment deep down in their nest, and bumble bees can warm themselves up by contracting their wing muscles rapidly after disconnecting them from the wings. A buzzing bumble bee sitting on a flower can be observed doing this.

These ways of circumventing weather enable bees to gather nectar and pollen when other insects can’t fly due to weather conditions.

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Weather Brings More Insects Into Houses

The weather can also affect where insects live. Many insects adapt to cold weather by migrating to warmer areas or finding a place to shelter. Spiders, cockroaches, and ladybirds are often seen more in homes following cold or wet weather.

Because there are more insects in summer, you may notice more coming into your home. This can attract larger spiders into your home as they look for their next meal.

Dry weather can also increase ants, mosquitoes, and grasshoppers, whose numbers multiply in hot weather.

Wet weather can bring mosquitoes, termites, and cockroaches into your house. Clear up any stagnant water to get rid of mosquito eggs. Spiders and ants can often invade your house when it is raining outside.

How Weather Affects Parasites

The marsh fritillary is parasitized by a tiny wasp that lays its eggs in the caterpillar. When the larvae emerge from their host in spring, they spin a cocoon around the dying caterpillar.

Here they pupate and develop into adult wasps, searching for more caterpillars to parasitize. If it is cold but sunny, the pupal parasites develop slowly, and when the adults emerge, there are no caterpillars left to parasitize.

However, if there is a dull, mild spell, the parasites and caterpillars are held back, and the wasps emerge to find plenty of hosts. The weather is crucial and may mean the difference between 10% and 90% parasitism of marsh fritillary caterpillars, with huge effects on adult numbers. 

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