Most adult spiders (as many as 85% of temperate zone species) are dormant during the winter, seeking shelter beneath the leaf litter. Their metabolism slows and their need for food is greatly reduced. Other species die at the end of the summer, and their eggs overwinter, protected inside silken sacs. A third, even smaller, group of spiders remains active through the winter.
Spiders’ body temperatures vary significantly, heavily influenced by their environment. Many spiders that remain active year round seek shelter in the subnivean layer between the ground and snow, where the temperature (+/-32°F.) is often warmer than the air. Occasionally, however, they do appear on the surface of the snow, where they are exposed to the wintery blasts of cold air.
Scientists don’t know exactly how these active spiders survive the cold. Some species can tolerate temperatures as low as -4° F.°. Glycerol acts as a type of anti-freeze for these arachnids, but its effect is marginal. In order to survive, some species bask in the sun and derive energy from their diet of snow fleas (a type of springtail) and other small prey, but these strategies don’t totally explain their ability to survive a New England winter. Species of spiders in the families Linyphiidae and Tetragnathidae (see photo) are often what you see crawling on top of the snow.
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Snow fleas, a species of springtail, are not a type of flea. Neither are they insects, though they are close relatives. During most of the year they live in the soil and leaf litter, consuming fungi and decaying vegetation. On warm winter days they appear on the surface of the snow, and are often described as “pepper on snow” due to their black color and tiny size (1 – 2 millimeters long).
Although they lack wings, they have two tail-like spring projections, or furcula, which are held like a spring against the bottom of their abdomen by a kind of latch. When the snow flea wants to move, the furcula springs downward, catapulting the snowflea as far as 100 times its body length. Snowfleas in the genus Hypogastrura possess three pinkish anal sacs which are usually located inside the snowflea, hidden from view. Just before jumping the snowflea everts these sacs from its anus. Their function has not been confirmed, but many biologists believe they serve as a sticky safety bag which prevents the snowflea from bouncing around when it lands.
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Although insects and animal matter make up less than 10% of the annual black bear diet, they are a crucial part of it. Black bears get most of their animal protein from ant brood, hornet larvae, tent caterpillars, march fly larvae, grubs (especially June beetle grubs), and snow fleas. Among the most preferred sources are bee and hornet larvae. Berries and other fruit don’t have a great amount of protein, but they do have some (blackberries = 2 grams of protein per cup). If the summer berry crops fail, insect brood is especially important, especially at this time of year, when bears are seeking protein, fats and carbohydrates, putting on as much as 30 pounds per week to sustain themselves through the coming months of hibernation.
When tearing apart a beehive, yellow jacket nest or bald-faced hornet nest (see photo), bears do get stung, particularly on their ears and faces (their fur is fairly impenetrable). Apparently the reward is worth the aggravation. After filling themselves with brood (and in some cases, honey) black bears shake vigorously in order to rid themselves of any insects that are caught in their fur.(Thanks to Alfred Balch for photo op.)
One rarely even thinks about snowfleas (a species of springtail, Hypogastrura nivicola) until snow falls and then starts to melt. This is when these tiny wingless arthropods that catapult themselves through the air with the aid of a fork-like structure, or furcular, seem to magically appear out of nowhere. They actually are present year round, but their dark color makes them visible against the white snow.
The great majority of snowfleas live in soil, feeding on fungi, algae, decaying plant matter and bacteria. They work their way to the surface of the snow, crawling up the trunks of trees, plant stems and side of rocks where an open channel allows their migration. Thousands can be found on melting snow, especially in tracks or other depressions. No-one is absolutely sure of why they exhibit this behavior, though some scientists feel that these migrations are triggered by overcrowding and lack of food. Eventually those that survive on top of the snow make a return trip down into the soil.
Formerly classified as insects, snowfleas are now categorized as hexapods, due to some features they have which insects do not.
Snowfleas are such remarkable little arthropods that they merit at least an annual post. The recent warm weather brought them up out of the leaf litter to the surface of the snow, where they constantly hurl themselves from one spot to another. If you don’t mind getting your knees wet, you can watch as snowfleas tuck their head down and catapult themselves through the air. Just before launching themselves, the snowflea everts three anal sacs from its anus. When the snowflea lands, these sticky appendages act like automobile air bags, absorbing the shock of landing as well as preventing the snowflea from bouncing around. There may be another function that they perform, but it is not known at this time what that might be. While there are many genera of snowfleas, only species in the genus Hypogastrura possess anal sacs.
We tend to associate snow fleas, a type of springtail, with winter, as that is when we can easily see their tiny black bodies against the white snow. However, these insects don’t magically appear when it snows – they are in the leaf litter and soil all year round. Snow fleas are considered to be one of the most numerous land animals on earth, with several hundred thousand inhabiting a cubic yard. Even so, it was with amazement that I found several piles of snow fleas at the base of my garage door this morning – it’s the wrong time of year, and most of the individual snow fleas were not scattered apart from each other. Several solid black patches of snow fleas, one patch measuring roughly 6” by 2 ½ ”, piled 1/8” high, had appeared overnight. Something about the warm, humid air this morning may have caused them to leave the safety of the forest floor and for some unknown reason gather in piles on the cement. Once the garage door was raised, the piles disappeared within five minutes, as each tiny snow flea catapulted itself several inches away and disappeared into fallen leaves.
What happens to insects this time of year? A few remain active, such as snow fleas, and some, like monarch butterflies, migrate, but the vast majority of insects overwinter in New England. The insects that stay here are susceptible to freezing due to the fact that they cannot control the temperature of their body. Some insects, such as woolly bear caterpillars, can tolerate having ice form in their tissues, but most insects go into a state known as diapause. When the days start getting shorter, these insects reduce the water content of their body, as water freezes at a high temperature compared to other liquids, and replace it with glycerol, which acts like antifreeze, protecting them from freezing. (Due to technical problems which hopefully will be resolved soon, I am unable to include a photograph with this post. My sincere apologies.)