An infestation of venomous false widow spiders has forced the closure of four schools, with some closed for almost a month.
Ellen Wilkinson Primary School, Star Primary School, Lister Community School and Rokeby School in Newham, east London, have been closed since Wednesday.
Parents have been told the infestation was discovered during a routine check by Newham Council’s environmental team.
A letter posted on Star Primary School's website says: "They believe that the infestation is contained to the outside of the building and that this needs to be treated immediately before the eggs start hatching."
The letter to Rokeby School parents says: "I have had to take the difficult decision to close Rokeby School to students and staff until Monday 29th October 2018.
"This is due to an infestation of spiders in the building that was discovered this morning.
"We have engaged a company to deal with and eradicate this pest, they have estimated that this will take up to three weeks."
All of the schools say the children will be given homework and study resources during the closures.
Ellen Wilkinson School says it is "exploring the possibility of using alternative venues next week".
‘radical and unnecessary overreaction’
The Natural History Museum websites says the noble false widow spider reaches a body length of 8.5mm to 11mm.
It was first recorded in the UK in the 1870s - probably a stowaway on cargo ships from its native Madeira and the Canary Islands.
The website added: "The pattern on their bodies is often described as 'skull-shaped', which probably doesn't help their negative reputation.”
It says that while their bite is venomous, it is not particularly potent and any pain is usually gone within 12 hours.
Wildlife charity Buglife said: "We consider this to be a radical and unnecessary overreaction to the tiny risk posed, indeed the spraying of the schools with toxic insecticides may be a higher risk."
Its chief executive Matt Shardlow said: "It is a shame that the education, and potentially the health, of these children is being harmed by this knee-jerk risk assessment."