Invasive brown spiders protect eggs by attacking wasps: study

Israeli researchers have discovered that brown widow spiders, a global invasive species, aggressively defend their egg sacs from parasitic wasps, offering insights into how certain species adapt and thrive in new environments with parental care, Ben Gurion University said in a statement on Wednesday.

In the study published in Proceedings of the Royal Society B, the researchers compared the brown widow spider, commonly found in urban areas such as fence posts and trash bins, with the native white widow spider, which lives in desert regions in the Middle East.

When wasps approached their silk-wrapped egg sacs, the brown widow tapped them, circled them protectively with legs, and aggressively attacked the wasps, capturing and either killing or removing them from the web.

In contrast, white widows only shook their webs to scare the wasps away.

The researchers also found that wasps are more likely to target the smooth side of an egg sac. Interestingly, as an effective deterrent, brown widow spiders cover the silk-wrapped egg sacs with protective silk spikes and increase the number of silk spikes after encountering wasps, hinting at an adaptive defense strategy.

The researchers concluded that the brown widow spiders employ behavioural defences and modifications to the egg sac structure to protect against the threat, providing an advantage over native species, potentially contributing to invasion success.