Resident Predators: Living With Spiders

A third of India’s population lives in urban spaces — cities and towns that are labyrinths of concrete, wires, and traffic. It is difficult for most of us to imagine our concretised homes as ecosystems that harbour a wide diversity of wildlife, but they are. Plants in our homes and neighbourhoods produce nutrients through photosynthesis; insects like aphids and planthoppers feed on plants materials; flies and cockroaches, considered by many to be pests, play the critical role of scavengers that break down organic materials. These home ecosystems also come with an incredible group of resident predators — spiders.

Like their human housemates, the spiders that inhabit India’s urban homes lead beautifully complex lives. Here’s a sneak peek into the lives of five of these spider families.

Pholcidae family

Cellar spiders from the Pholcidae family are possibly the most common spiders we encounter in our homes. These spiders have tiny bodies equipped with eight exceptionally long, thin legs. They typically set up their web-based workplaces in wall and ceiling corners. While the webs look messy, they are highly functional and rely on their irregular structures to ensnare prey. In my home, cellar spiders have found two highly productive spots. The first location is the ceiling directly above a light that comes on every evening and attracts a diversity of flying insects (including mosquitoes). When these insects fly straight up from the lamp, they get trapped in the spider’s strategically placed web. Hardly three feet off the ground, the second location is a corner directly above a potted money plant. The soil around this pot is a hotbed for emerging soldier flies, who often fly straight into the web above them. Another intriguing feature to watch in cellar spiders is their diligent motherhood. Cellar spider mothers wrap their eggs in silk and create an “egg sac”. The mother then carries this silken cradle in her chelicerae (mouthparts) for up to three weeks.

Uloboridae family

Other common inhabitants of wall corners in our homes are spiders from the Uloboridae family. These spiders build 2D orb-webs often placed horizontally in an area frequented by flying insects. Unlike orb-weaving spiders from the Araneidae family, Uloborids do not produce glue to make their webs sticky. Instead, these eight-legged physics enthusiasts leverage intermolecular forces to catch their prey. Uloborids have a specialised organ called the cribellum that produces “cribellate silk” that the spider extrudes into microscopically thin threads. This ridiculously fine cribellate silk is integrated into the basal orb-web structure. When unsuspecting prey falls onto the web, the nanofibers of cribellate silk stick to the insect through van der Waals forces (a force of attraction between molecules). The spider’s cribellate nanofibers also create capillary forces (movement of liquid into narrow spaces) with the thin layer of wax on the skin of its insect prey. With its silky arsenal seemingly sufficient, this is the only family of spiders that does not produce any venom.

Oecobiidae family

Spiders of the Oecobiidae family are omnipresent urban residents. Their name is derived from the Greek words “oikos” meaning home, and “bios” meaning life, referring to their penchant for dwelling inside human homes. Despite their ubiquitous nature, they often go unnoticed because of their size. Oecobiidae spiders are tiny (as a small black ant) and require a fair amount of searching before they are found. They typically inhabit small coin-sized webs in corners where walls meet the ceiling. These fascinating little spiders also produce cribellate silk to catch a wide diversity of prey ranging from flies to ants.

Theridiidae family

Waiting patiently, in less conspicuous spots like the underside of a table or close to a door hinge, are tangle-web spiders from the Theridiidae family. These spiders build intricately complex 3D web structures to catch their prey. Sitting in the middle of this web is a spider with a roundish abdomen that appears to be most of its body — it looks like a colourful ball bearing with thin legs. While these webs may appear messy from a distance, a closer look will reveal a rather hygienically maintained iridescent silken art installation that shimmers when light falls on it. The 3D maze of silk acts as a hunting tool to catch flying insects, a web fortress to protect the spider from aerial predators and a safe spot for the spider to suspend her egg sac.

Salticidae family

Not all urban home-dwelling spiders build webs. Jumping spiders from the Salticidae family are active hunters that walk around the house in search of their next meal. To enable locomotion, spiders pump lymphatic fluid in and out of their legs to move their legs (hydraulics!). In the stalkily built jumping spider, the hydraulic action in its hind legs also enables the spider to jump 10-50 times its body length - a helpful trait to pounce on unsuspecting prey. Another characteristic trait of jumping spiders is their large frontal eyes. Aside from the function of breaking hearts, jumping spider eyes provide them with incredible eyesight. The two large frontal eyes focus on objects like prey, threats, or curious humans. The secondary frontal eyes next to the large eyes let the spider detect motion. Using a combination of these signals, the spider gauges distance and hunts with a level of prowess that would make any house cat wish it had hydraulic legs instead of muscular ones.

Despite our best (possibly unwitting) efforts to “shelter” ourselves from the natural world, nature has a way of reminding us that humans are just one thread in the complex web of life. It may not be possible to undo the rampant urbanisation all around us. What we can do is get to know our fellow non-human urbanites, starting with the ones that share our homes.