Silver Spiders (Argyrodes sp.), also known as dew-drop spiders, don’t make their own web. Instead, they are dependent on larger spiders for their food and can often be found on webs of larger orb-weaver spiders. Webs of Giant Wood Spiders (Nephila sp.), Signature Spiders (Argiope sp.), Common Orb Weavers (Neoscona sp.), Spiny Orb Weavers (Gasteracantha sp.) and even Social Spiders (Stegodyphus sarasinorum) are good places to find Silver Spiders.
Silver Spiders make a meal of small prey which are trapped by the webs of the larger spiders, by stealing the prey. At times, they start feeding on a large prey even as the web-owner is feeding on it. Therefore, they are also referred to as kleptoparasites.
Though they don’t make webs to trap prey, Silver Spiders are very capable of producing silk. This capability is used when they are ready to lay eggs. They make seed-shaped egg sacs containing about 20-30 eggs. The egg sacs, depending on the species, are orange, white or dark brown, and are typically suspended from a few lines of silk. The shape and colour of the egg sacs make them difficult to spot by possible predators. Female Silver Spiders stay with the egg sac for about a week and then disappear, leaving the sac alone.
Moths of the genus Miltochrista (family Erebidae; subfamily Arctiinae) have been observed to lay their eggs on Silver Spider egg sacs! Though this behaviour has not been published in any scientific journal so far, it has been documented twice at our farm.
On 25th December 2021, 8:30 pm, a moth started laying eggs on a spider egg sac. It started from the egg sac and continued to lay eggs on the web strings which were holding the egg sac. In about an hour, the moth laid more than fifty eggs! At this point in time, the exact reason for such behaviour is not known – one can only surmise that the moth was using the egg sac of a Silver Spider to lay its own eggs on, as it is reasonably safe from predators.
It did not take long for the caterpillars to hatch. In about a week i.e. on 1st January 2022, the moth larvae were out and seen moving about on the spider silk. It is interesting to note that it took about 3 months for the spiderlings of the Silver Spider to emerge. In the meantime, the egg sac gave a moth an opportunity to breed! I found this very fascinating, and more such observations could help us understand this process better.