Although orchard orbweaver spiders (Leucauge venusta) are one of the most common spiders in Massachusetts, they are small and easy to miss. You might spot one in the center of a wagon-wheel shaped web. If you look closely, you may notice it has green legs and orange, yellow or red markings.
Orchard orbweavers emerge in the spring. They spend the summer eating, growing, molting and mating. The females spin webs (the males do not) that look similar to a Halloween decoration – with a central hub and 30 or more “spokes” radiating out from the center. The outermost part contains more than 60 sticky spirals. The female rests upside down in the center and waits for vibrations that indicate something has been trapped. When it detects the right vibrations, the spider rushes out to grab the prey. It ignores, for example, the flailing of an angry bee, but responds immediately to the vibrations of a fly’s wings.
Orchard orbweavers eat their own web each evening. After they digest the web, they store the silk as liquid in internal silk glands. They use structures outside the body, called spinnerets, to make new threads. Each day, in the darkness of early morning, they construct a new web. Despite the intricacy of the web, it takes only about an hour to build! Although similar, each spider’s web is unique, and scientists who study these spiders can tell which spider built which web just by looking.
Hummingbirds, vireos and warblers may steal webs to use for nesting material. But the spider knows how much silk it has. If the web has been damaged, providing it with a smaller web to eat in the evening, it constructs a smaller web the next day. Spider silk starts out as a water-soluble liquid stored inside a spider’s body, but it transforms into a non-water-soluble thread outside the spider’s body. Scientists think that pulling on the thread as it leaves the body realigns the molecules into a solid.
Orchard webs with the most silk strands in the center attract the most prey. Some strands reflect ultraviolet light, even in the dark. This is helpful, since these spiders are mostly nocturnal. Many insects see ultraviolet light, and many flowers reflect ultraviolet light. Some insects may be attracted to the ultraviolet light of the web. When these colorful spiders sit in the center of their web, they entice insects to visit. Some scientists speculate that the brightly colored spider resembles flowers the insects visit for nectar.
Male spiders interested in mating with a female must be careful as they approach her web – or they might end up as her dinner! The male approaches the outer part of the web. He announces his intentions by plucking or tapping on the threads of the web. Eventually, the female may allow the male to enter the web. The male transfers sperm to leglike appendages called pedipalps near his mouth. He makes his way across the web and inserts his pedipalps into the female’s reproductive plate on the underside of her abdomen.
Males die soon after mating while females construct egg sacs of fluffy orangish silk on protected leaves or twigs near the web. Each sac contains several hundred dark orange eggs. As long as the weather is warm, the female produces egg sacs. When the temperature cools, the spider’s metabolism slows and it dies. But spiderlings hatch in the egg sacs, and emerge in the spring to repeat the cycle. Most spiderlings do not survive long.
Orchard orbweavers catch and eat small insects such as mosquitoes, flies and gnats. Once an insect gets stuck in the web, the orbweaver uses her fangs to bite the insect, delivering neurotoxins to halt struggling and digestive enzymes that cause the insect’s tissues to liquefy. After the digestive enzymes have done their work, the spider contracts her stomach muscles to slurp up the liquified remains like a milkshake. Hairs at the spider’s mouth strain out particles that have not liquified. The spider repeats this process until all that is left of the insect is a small undigestible ball.
Although orchard orbweavers are helpful to humans, ridding us of insect pests, they have many enemies. They are easy prey for birds and reptiles, bats and rodents. Even other spiders eat them. Parasitic wasps sting and paralyze these spiders, then lay an egg on the spider’s abdomen. The spider recovers and continues its daily routine as the wasp larva sucks fluids from the spider’s body. When the larva gets large enough, it injects the spider with a hormone that causes the spider to stop hunting. It soon dies. The larva sucks up the remaining abdominal fluid until only the spider’s exoskeleton remains.
In 1973, scientists took two orchard orbweavers into space aboard Skylab 3 and studied their ability to build webs in zero gravity. At first, the usually oval webs were rounded because the spiders could not use the pull of gravity on their bodies to guide construction. But after only three days, the spiders adapted to their weightlessness and built excellent oval webs.
How come orchard orbweavers do not get stuck in their sticky webs? Scientists are not certain, but they know some things: These spiders make many different kinds of silk. The strands that radiate out are not sticky, so the spider may know which threads to avoid. In addition, orchard orbweavers have three claws on their feet. They provide traction and help them move along the threads.
Charles Darwin named these spiders Leucauge venusta. Leucauge means “with a bright gleam.” Venusta refers to “beauty,” since Venus is the Roman goddess of love and beauty. Whether you think these spiders are beautiful may depend on how you feel about spiders in general. Three things are certain, though: These docile spiders flee when threatened, they are harmless to humans and they rid us of many annoying insect pests.
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Jeanine Farley is an educational writer who has lived in the Boston area for more than 30 years. She enjoys taking photos of our urban wild things.
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