Raising Spiderlings: The Best of Jumping Spider Brood Care

Parental care is a vastly diverse set of natural phenomena that have one central theme — an animal goes out of its way to increase its offspring’s likelihood of success. Octopuses, for instance, have been well-documented to starve themselves as they diligently watch over their young. Humans nurture their infants with nutrition through lactation, and in some cases, continue to provide nutrition to their children even 30 years later. While popular stories like the octopus and our own experiences as humans readily come to mind at the mention of “parental care”, another fascinating group of parents that often go undiscussed are spiders. Spiders bring their young into the world in the form of eggs. When eggs from a clutch hatch together, the collective term for the newly emerged younglings is a “brood”. The parental behaviour that follows this is typically called “brood care”. The world of brood care in spiders is filled with incredible stories. For instance, wolf spider mothers (Lycosidae) carry over a hundred hatchlings on their backs for weeks. In this story, however, we focus on jumping spiders (Salticidae), a family of spiders that present parental behaviours that warm the heart and routinely blow the mind. Jumping spiders have more to them than their tiny sizes and dewy eyes. Most species in this family have been found to carefully wrap their eggs with silk and stand guard to ward off predators, parasites, and gaze judgingly at flash photographers.

The jumping spider family falls comfortably inside the set of spiders that do not build webs. These leaping predators move around during the day searching for their next meal and pounce on prey with a jump that justifies their name. Though they do not create webs, these spiders still produce silk that comes in handy for constructing a secure space for their eggs. Jumping spider egg sacs are often tailored to their microhabitat. Some egg sacs even share interesting relationships with the plants beneath them. Jumpers in the genus Phaeacius build thick silken egg sacs that are covered with small bits of detritus. The egg sac of Phaeacius blends seamlessly with the tree bark beneath it — an ingenious way of hiding their young in plain sight. The genus Lyssomanes (distributed across the Americas) builds a sparse silken egg sac with its eggs spaced generously on the silken structure. Research has found that this structure might improve exposure of the eggs to volatile antimicrobial compounds released by the leaves on which the egg sac is built. This is a fascinating immunological strategy to protect the eggs and could very likely be found in the Indian genus Hindumanes (closely related to Lyssomanes). A single observation of brood care in Hindumanes revealed the egg sac structure to be nearly identical to that of Lyssomanes. The Hindumanes sp. was also found with her egg sac on the underside of a Colocasia esculenta (taro) plant (with well-documented antimicrobial properties).

Some species of jumping spiders like Myrmarachne melanotarsa live in social groups with multiple nests connected with strings of silk. These nest collectives are typically found on tree trunks close to the arboreal nests of Crematogaster ants. The benefits of living close to a highly territorial genus of ant include protection from potential predators that could easily mistake the spiders for ants. However, this strategy comes with the real danger of having their nests swarmed by Crematogaster ants that will readily feed on the spider’s eggs and juveniles.

Cosmophasis bitaeniata, a jumping spider that chemically mimics the weaver ant Oecophylla smaragdina, kicks “exploitative parenting” up a notch. This spectacularly coloured species of jumper is known to feed on weaver ant larvae and subsequently acquire the chemical signature of the ant larvae consumed. It uses this chemical disguise to gain access to the secure inner chambers of weaver ant nests. Several studies conducted in Australia have found the spider’s egg sacs safely built inside the safety of weaver ant nests! This highly lucrative deal for the spider means its eggs hatch inside the nests of an intimidatingly dominant ant species. To make the deal even more delectable, these nests are also the homes of the ant colony’s larvae; spiderlings that hatch inside these nests also have access to a generous source of nutrition in the form of protein-rich ant larvae.

The concept of lactation in its strictest sense is limited to mammals that produce a protein-rich substance in their mammaries and provide this “milk” to their young. Stretch that definition enough to replace the mammaries with an epigastric furrow (reproductive organs of a spider), and voila, you have a jumping spider that lactates. A group of researchers from the Chinese Academy of Sciences found that Toxeus magnus, a species of ant-mimicking spider, produces a milk-like substance from its epigastric furrow. For the first week, the mother deposits drops of the milk-like substance onto the inner lining of the nest for the spiderlings to ingest. From the second week onwards, the mother stops depositing the substance on the silk; instead, the spiderlings suck milk directly from the mother’s epigastric furrow. The mother continues to feed the spiderlings until they are subadults. The team of researchers also found that a newly hatched T. magnus prevented from accessing the milk-like substance dies within ten days — highlighting that this is a vital process in the development and survival of this species.

Closer to home, Brettus cingulatus is a species of jumping spider that is known for guarding its egg sac (evidenced by a large volume of photographs shared on social media platforms like Instagram). The spider is seen in its characteristic position with folded legs typically sitting on its mesh-like silken egg sac. Several photo-documented observations suggest that the male spider remains in the vicinity of the female and the brood, keeping a watchful eye on them from afar. In another short paper titled “Do female Brettus cingulatus (Araneae: Salticidae: Spartaeini) feed their young?” the authors hypothesize that Brettus might be lining its egg sac with a protein-rich substance, on which the newly emerged spiderlings feed.