Bedbugs are on the increase in many developed countries, including the UK, research has found.
The insects had been almost wiped out
The tiny blood-sucking insects were thought to have been virtually eradicated two decades ago.
But an expert writing for the Institute of Biology believes they may have developed resistance to pesticides.
Since 1995 there has been an unexpected increase in reports of infestation in Britain, the US and other developed countries.
Writing in the Institute magazine, biologist Clive Boase, of the UK company Pest Management Consultancy, said that since the mid-1990s reports of infestations had almost doubled annually.
The degree of reaction to the bite
For some people it has no effect
Many develop an itchy swelling which may last for weeks
Exceptionally heavy levels of bug
feeding have been associated with anaemia
However, he said numbers were still nowhere near those of pre-war levels.
Bedbugs, which measure up to 5mm across, thrive in warm surroundings.
They make their homes around mattress seams, in bed frames, behind headboards or skirting boards, and within furniture and electrical fittings.
Even when deprived of blood, individual bugs can survive a year or more - allowing infestations to persist in empty properties or stored furniture.
When conditions are right, and food is in plentiful supply, numbers can rapidly spiral.
Mr Boase said it was unclear exactly why the insects had made such a successful comeback.
Some people think the growth in international travel may be a factor.
But Mr Boase said the bugs identified in recent reports from London were the domestic rather than tropical variety.
Sales of second-hand furniture, in which the bugs may be hiding, were another
possibility. But this was unlikely to account for the growth of infestations in
It has also been suggested that the re-emergence is in some way linked to a change in insecticide sprays.
Previously, sprays often killed many types of insect, regardless of whether they were the primary target.
But sophisticated modern forms are more highly targeted, only killing the insects they are designed to be deployed against.
Thus, the theory has it, bedbugs are less likely to suffer "collateral" damage from sprays designed to kill off other pests such as cockroaches and ants.
However, Mr Boase said it was unlikely that kitchen-focused spray treatments
would have ever held bedbugs in check.
He favours the idea that the bugs are becoming resistant to pesticides.
Research from East Africa has shown an association between the use of pesticide-treated mosquito nets and the growth of resistance in bedbugs.
The pesticide involved, pyrethroid, was a type widely used in bedbug sprays
in developed countries.
Mr Boase said: "Such a process, perhaps coupled with some of the other factors above, may explain why bedbug infestations are often difficult to control, and as a result are increasing.
"However, until detailed resistance tests are conducted on temperate bedbugs, this must remain speculation.
"Hopefully, the current upswing in bed bug infestations is no more than a transient event in our erratic move towards a largely pest-free urban environment.
"Insecticides with alternative modes of action, improved detection techniques and
increased vigilance should help to turn this upswing around.
"However, it does provide us with a salutary lesson about the resilience of urban pests."