Brown widow spiders protect their young from parasitic wasps

In the web of life, survival demands strategy. For the brown widow spider, survival hinges on one essential task – protecting its offspring.

These invasive spiders have spread across urban landscapes, thriving in hidden corners beneath garbage cans, fence posts, and building nooks. Their success may not just be about adaptability but also about fierce maternal instincts.

Valeria Arabesky and her team at Ben-Gurion University of the Negev decided to dig deeper. In a study published in the journal Proceedings of the Royal Society B, they examined how brown widow spiders defend their egg sacs against parasitic wasps.

The findings reveal that these spiders don’t just rely on luck – they actively fight back.

Maternal instincts of brown widow spiders

For many species, eggs represent a vulnerable stage of life. Defenseless and stationary, they become prime targets for parasites and predators.

“For creatures that start their life as eggs, such as spiders, parental protection can be crucial. The eggs themselves are defenseless and very attractive to parasites and predators, thus their parents are their only hope for survival,” noted Arabesky, the study’s lead author.

Brown widow spiders take this to heart. While some spiders abandon their eggs, brown widows do the opposite. They guard them with vigilance, patrolling the web and encircling their egg sacs with protective legs.

The battle begins: Wasp vs. spider

Tiny parasitic wasps, known as Philolema latrodecti, target spider eggs. They approach spider webs, seeking a chance to lay their own eggs inside the silken sacs. What happens next? A clash of survival strategies.

Brown widow spiders respond with aggression. They don’t wait. They tap their egg sacs, sending vibrations that warn the wasps to stay away.

If that doesn’t work, they escalate. The spiders capture the wasps, killing them and tossing them out of the web – without even feeding on them. It’s not about hunger. It’s about protection.

White widow spiders, on the other hand, adopt a less aggressive stance. They shake their webs violently, hoping to dislodge the intruders. But shaking only goes so far. While it can fend off some wasps, it lacks the direct impact of the brown widow’s lethal approach.

Silk spikes: The secret weapon

Beyond aggression, brown widow spiders wield another weapon – silk spikes. They cover their egg sacs in dense, sharp silk protrusions. The spikes form a physical barrier, complicating any wasp’s attempts to penetrate the sacs.

The researchers tested this strategy. They carefully removed spikes from some sacs and left others intact. Then, they introduced the parasitic wasps. The results? Wasps consistently preferred the smooth, spike-free sacs, laying their eggs there without hesitation.

Spikes, it turns out, aren’t just for show. They serve a vital purpose. Brown widow spiders use them to disrupt wasp attacks, giving their eggs a fighting chance.

How brown widows adapt to threats

Brown widow spiders don’t just sit back and wait for wasps to attack – they adapt. When wasps linger nearby, these spiders go into defense mode, thickening the silk spikes around their sacs. It’s a calculated move, a way to reinforce barriers when threats increase.

This behavior suggests a level of environmental awareness. Brown widows aren’t passive creatures. They assess their surroundings, identify potential dangers, and adjust their defenses accordingly. That level of adaptability may explain why they’ve become such successful invaders.

Urban spaces help widow spiders

Urban environments provide the perfect stage for this spider-wasp showdown. Buildings, fences, and garbage cans create hiding spots for spiders, while also attracting parasitic wasps. The stakes rise in these crowded, chaotic spaces.

Brown widow spiders thrive here. Their dense, spiked egg sacs blend into the urban clutter, camouflaged yet heavily fortified. White widow spiders, accustomed to open desert habitats, struggle to keep up. They lack the silk spikes.

They lack the aggressive tactics. In the end, they lose more eggs to wasps.

A war without end

The battle between brown widows and wasps isn’t just about survival. It’s about control – of space, resources, and control of life itself. Brown widow spiders fight this war with silk, with legs, with sheer tenacity.

Their relentless defense strategies may hold a deeper lesson. Invasive species like brown widows don’t just spread through numbers. They spread by mastering the art of survival – by finding new ways to shield their young, by adapting, by refusing to back down.

Future research directions

Arabesky’s study raises more questions than it answers. Are other invasive species using similar tactics to protect their offspring? Could these strategies help explain how certain species dominate new habitats? And what role does parental care play in the success of invaders?

These questions open the door for further research. Brown widow spiders may have set the stage, but they’re just one piece of a larger puzzle.

As invasive species continue to reshape ecosystems, scientists may find that the fight for survival is more complex – and more intense – than anyone ever imagined.

The study is published in the journal Proceedings of the Royal Society B: Biological Sciences.

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