Almost every spring we see the same pattern across St Albans, Watford, Hemel Hempstead and the surrounding villages: a run of mild days in March or early April, and suddenly there are trails of small black ants along kitchen worktops, under skirting boards or marching out from behind the dishwasher. It's a seasonal nuisance, not bad housekeeping — and there are a few simple reasons it happens at the same time each year.
Why ants appear in spring
The UK's common black garden ant (Lasius niger) spends winter dormant in the nest, deep in soil, under paving slabs or in cavity walls. As soil temperatures rise above roughly 10°C, workers begin foraging again — and a house wall warmed by spring sun is one of the best food-scouting routes a colony can have. Once a single worker finds crumbs, pet food or a sugary spill, it leaves a pheromone trail and within hours you can have a steady line of ants.
The mistake most people make
Reaching for a shop-bought spray feels satisfying, but it usually makes things worse. Surface sprays kill the visible workers but never reach the queen, so the colony simply sends more — often via a different entry point. Worse, some repellent sprays cause the colony to bud into multiple satellite nests, turning one problem into three.
What actually works
- Wipe down the trail with hot soapy water to break the pheromone scent, but leave the entry point itself alone.
- Place professional-grade gel bait at the entry point — workers carry it back to the queen and the whole colony collapses within a week or two.
- Seal obvious entry routes (around pipework, airbricks, door thresholds) once the colony is dead, not before.
- Keep pet bowls off the floor overnight and store sugar, honey and jam in sealed containers through spring and summer.
If you've had ants in the same spot for two springs in a row, the nest is almost certainly in or under the building and won't go away on its own. A single bait treatment from a Hertfordshire technician will usually clear it permanently — far cheaper than another year of shop sprays.