After previous sightings in Buckinghamshire, it is feared the species may be moving east, further into the city.
The ants were first seen in Britain in 2009 when around 35,000 appeared in a residence in Gloucestershire.
Resembling ordinary black ants, though reportedly harder to kill, the insects are drawn to electrical outlets such as plug sockets, where they nestle and can cause house fires.
First identified as a species 20 years ago as Lasius neglectus, the creatures’ compulsion to follow electricity is said to be stronger than its need for food or drink.
Conservator Brain Ridout told the BBC the insects come in much greater numbers than black ants, and warned: “There will be ten to a hundred times as many of them.”
Resistant to traditional insect poison, a National Trust adviser told The Telegraph the ants “could easily establish themselves in Britain”.
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