Dancing, Deception and Cannibalism: The myths and realities of Maryland spiders
From their unique mating rituals to their importance for biomedical research, spiders are fascinating yet highly misunderstood creatures.
Maryland is home to more than 270 species of spiders that work hard both as predator and prey. A recent study published in the Science of Nature estimated that the world’s spider population consumes 400-800 million tons of prey in any given year. More than 3,000 bird species dine on spiders, and some, like the ruby-throated hummingbird, use spider silk to make their nests strong and stretchy.
Spiders belong to a group of animals known as arachnids. This group also includes mites, scorpions and ticks. Arachnids have two main body segments and eight legs, and lack wings or antennae. Worldwide, there are more than 50,000 species of spiders, from the giant goliath birdeater tarantula to the omnivorous Bagheera kiplingi jumping spider.
The majority of spider species have venom designed to paralyze or kill their prey. Researchers use spider venom to create drugs to kill cancer cells, prevent stroke-induced brain damage and treat chronic pain. In Maryland, only two species of spiders have medically-significant venom, that is, venom that often causes negative reactions in humans: the northern and southern black widow.
Spiders produce seven types of silk, each with different structure and function. No one species is able to make all seven types, however. Silk is produced within glands and is gently eased from the back of the spider by its legs. Fun fact: only around 50 percent of spider species create webs.
Spider silk is elastic, strong and resilient. It can absorb three-times more energy than Kevlar and is very light in comparison. Spider silk has appealed to humans for thousands of years. Biomedical researchers are studying spider silk to create bio-adhesives and lightweight armor, mend broken bones and repair damaged nerves. Currently, this research is limited by the inability to produce mass quantities; genetically modified goats are being used to meet some of the demand.
Date or dinner?
Male spiders often are significantly smaller than their female counterparts. So, many males have a tough task of convincing potential partners that they are more than just a meal. Because of this issue, spider species around the world have evolved captivating mating rituals.
Jumping spider males are well-known to woo any lady they meet, regardless of species. Their mating rituals include elaborate dances with lots of abdomen (butt) wiggling, arm flailing and vibrations designed to make the right lady go crazy. Unfortunately for the male, if the female doesn’t like his moves, he can become her next snack.
Many other species rely on vibratory signaling to attract potential mates. These include the black widow, several species of orbweavers and some wolf spider species.
The black widow is the only native Maryland spider that is dangerous to humans. All other venomous spiders here either have too little venom to affect people, or their venom is specially adapted for their prey.
Spider bites are actually quite uncommon. Most only bite humans in self-defense and rarely bite more than once; multiple bites are usually caused by insects such as bedbugs, chiggers, fleas, mites and ticks.
Male nursery web spiders court ladies by presenting silk-wrapped invertebrates as nuptial gifts, which increase his chances of being accepted by the female. The larger the gift, the longer he might have to spend with her. Unfortunately, some deceitful males present worthless gifts—cotton, exoskeletons, twigs—wrapped in silk. If the female catches wind of the fake gift, he also may become a meal.
Spiders come in many colors, shapes and sizes. In the late summer and fall, some of the most visible are the orbweavers, which create the quintessential orb-shaped web. Charlotte from the children’s novel Charlotte’s Web was modeled after the barn spider (Araneus cavaticus), an orbweaver that is also found in Maryland.
One of the most colorful species is the marbled orbweaver, (Araneus marmoreus) which has a mottled yellow and black back end, and orange, striped legs. As it ages, the colors fade into hues of orange. Orchard orbweavers (Leucauge venusta) are often seen in backyards and gardens.
Another large and visible group is the jumping spiders. These typically have flat faces and large, front-facing eyes. They don’t build webs except for occasional molting or mating retreats, and they spend their days hunting down food wherever they can find it. Like Spider-Man, this group often uses silk draglines as they plunge off ledges. One of the common jumping spider species found in and around Maryland homes includes the bold jumping spider (Phidippus audax). This species is easily recognized by its iridescent blue or green chelicerae (mouthparts).
The big, brown and hairy spiders fall into several groups: nursery web spiders, grass and funnel spiders, fishing spiders and wolf spiders. Funnel and grass spiders tend to have large, visible spinnerets on their back end. Some species create large, funnel-like webs where they lay and wait for prey to walk by. Wolf spiders are well-known for their maternal tendencies. The females carry their egg sacs and later their young, providing a lot of care. When startled, the female often rears up and the young scatter. Once the danger is gone, she gathers up her young. Fishing spider females can grow rather large, and aren’t always found around water.
Overall, the world of spiders is unique and diverse, and we still have much to learn about this amazing group of animals.
Article by Kerry Wixted—wildlife education specialist.
Appears in Vol. 20, No. 4 of the Maryland Natural Resource magazine, fall 2017.