An infestation of venomous false widow spiders has forced the closure of four schools - some 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".
What is the false widow spider?
The venomous insect, which has been in Britain for the last 130 years, is a cousin of the deadly black widow spider, but unlike its close relative, its bites are not fatal to humans.
There have been isolated cases of people needing hospital treatment after being bitten, but generally, symptoms are typically limited to pain around the bite and swelling.
Most serious cases are often due to an allergic reaction to the spider’s venom.
While their bite is venomous, it is not particularly potent and any pain is usually gone within 12 hours.
The Natural History Museum websites says the noble false widow spider reaches a body length of 8.5mm to 11mm.
They are dark-coloured with distinctive cream markings, round bodies and reddish-orange legs.
The false widow, or steatoda nobilis, is native to Madiera and the Canary Islands.
It is believed it may have arrived in England in the late 1800s as a stowaway critter on cargo ships.
It is one of roughly 670 different species of spider present in Britain, according to the British Arachnological Society (BAS).