Spiders produce different types of silk for different purposes, including draglines, egg sacs, ballooning, building a web and wrapping prey. Much of the silk spiders use to spin webs has a sticky consistency, in order to catch flying insects. It turns out that sticky silk isn’t the only reason spider webs are such efficient insect catchers.
According to scientists at Oxford University, not only is much of a spider’s web silk sticky, but it is coated with a glue that is electrically conductive. This glue causes spider webs to reach out and grab all charged particles that fly into it, from pollen to grasshoppers. Physics accounts for the web moving toward all airborne objects, whether they are positively or negatively charged.
According to Prof. Vollrath of Oxford University, electrical attraction also drags airborne pollutants (aerosols, pesticides, etc.) to the web. For this reason, it’s been suggested that webs could be a valuable resource for environmental monitoring. (Thanks to Elizabeth Walker and Linda Fuerst for introducing me to this phenomenon.)
It is not unusual to come across a rolled-up leaf – the larvae of many moths create shelters in this fashion, using silk as their thread. Less common, and more intricate, are the leaf “tents” of sac spiders. With great attention paid to the most minute details, a female sac spider bends a leaf (often a monocot, with parallel veins, as in photo) in two places and seals the edges (that come together perfectly) with silk. She then spins a silk lining for this tent, inside of which she lays her eggs. There she spends the rest of her life, guarding the eggs. She will die before the eggs hatch and her body will serve as her offspring’s first meal. (Thanks to Ginny Barlow for photo op.)
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At this time of year, many new sterile fern fronds have “fern balls” at their tips – something has taken the last few inches of the tip of the frond and stitched it together into a ball-shaped shelter bound with silk. If you open one of these balls, you may find frass – droppings from the immature insect that was dwelling within the ball while consuming the terminal leaflets of the fern. Sometimes, but not always, you’ll find the larva responsible for the frass. Many species of ferns, as well as other plants, are host to many species of larvae, and many of these larvae are immature moths. Pictured is Christmas Fern, Polystichum acrostichoides, which is likely the host of the larva of Herpetograma sphingealis, the Serpentine Webworm Moth, or its close relative, H. aeglealis. Larvae live in these shelters for about a month before pupating and emerging as small, brown moths.