Guide to woodworm
Woodworm is a generic term for different species of wood boring insect. Different species have vastly different implications in respect of risk of structural damage to timber within buildings, and it is therefore essential in the first instance both to identify species, and also whether it is active or not.
Identification can be based on a number of factors - size and shape of exit holes (formed where beetle leaves timber), size shape and colour of bore dust (otherwise known as frass), is the frass fresh, type of timber, position of holes/damage, is any other decay present, in sapwood or heartwood, are any adult beetles present?
If it's not active or there is no risk associated with the species of beetle, it doesn't need treating.
Bark borer beetle (Wayney edge borer/Ernobius mollis). This is principally a forest beetle and burrows through bark and the superficial sapwood just beneath it. Timber beams/joists etc. in structures will sometimes have corners with a waney edge, i.e. where there is still some bark, and if that has had this beetle within it, it will look like insect attack.
It is however a forest beetle and the timber are not at risk, so beyond removal of the bark, it doesn't require treatment.
Others like common furniture beetle (Anobium punctatum), uniform round holes typically 1.5mm - 2mm dia. can tunnel through the sapwood and cause greater damage.
Insects like Deathwatch Beetle (Xestobium rufuvillosum) can be more damaging than CFB, although are rarer, being limited to oak and preferring partly decayed timbers. These are larger (circa 3mm dia.) and can tunnel extensively through sapwood and heartwood.
What about treatment? Well there is a life cycle of 2-5 years, whereby the beetle lays an egg, the larvae then hatches, burrows into the wood, tunnels around feeding and growing, before becoming a pupae, from which the beetle emerges and exits the timber, then flying around, mating and laying eggs for the cycle to start again.
They are treated with contact insecticides or ingested insecticides. You can only really apply this to the exterior of the timber (contact), or drill in and inject it (injected). This can mean that treatment is applied and the life cycle may only be broken a number of years later when a beetle emerges.
As with many things, best to get the right advice on such matters.