The Dean Academy in the Forest of Dean, Gloucestershire, has identified a number of false widow spiders in the school's computer block, as well as other areas.
A letter to parents on the school's website confirmed that the school would be closed tomorrow.
Vice principal Craig Burns said the academy had taken immediate pest control advice on discovery of the spiders. The letter posted online today read:
We have identified an issue with false widow spiders in the academy in our ICT block and therefore took immediate advice from pest control.
We therefore made the decision to close the ICT block for the whole of today so that pest control could fumigate the area.
Unfortunately, during this afternoon there have been further false widow spiders identified in other areas of the academy.
More top news
On the Tonight programme, presenter Kylie Pentelow investigates how much sun exposure is essentially too much, as experts disagree.
A woman in her 80s, from Bristol, lost thousands of pounds following a telephone scam that falsely suggested she owed money to the HMRC.
Numbers of A-level exams awarded top grades have risen for the first time in six years, summer results show.