Ticks and fleas after summer

Autumn is peak season for adult ticks

The common assumption is that tick season ends with summer. It does not. Summer is when nymphs — the tiny juvenile stage — are most numerous, which is why summer gets the warnings. Autumn is when adult blacklegged ticks are most active, and an adult tick is far easier to find on a body check than a nymph the size of a poppy seed.

Ticks quest for a host whenever the air is consistently above freezing and the ground is not snow-covered, with activity beginning at roughly 4 to 10 °C. A mild, damp November afternoon in southern Ontario, Nova Scotia or the Fraser Valley is working tick weather.

In Canada, 95.3% of Lyme disease cases occur between May and November — but cases have been recorded in every month of the year. The season narrows in winter; it does not close.

What to keep doing after Labour Day

The autumn routine is the summer routine, done with less conviction — which is the problem. Keep doing the two things that matter most:

• Body checks after being outdoors. Adults are larger and easier to spot, so a check in October is more likely to succeed than the same check in July.
• Keep pets on prevention. Stopping a dog's or cat's preventive in September because “the season is over” removes protection during the adult tick peak. Talk to your veterinarian about how long to continue in your region rather than guessing.

Leaf litter is the autumn-specific hazard. Raking, clearing gutters, and walking through unmown edges all put you in exactly the habitat adults use. Gardening in November deserves the same precautions as hiking in June.

How to do a body check  ·  Yard and habitat  ·  If you find one attached

Winter does not kill ticks

Ticks are not killed off by the first frost. They shelter under leaf litter and snow, which insulates rather than exposes them, and they resume questing during thaws. A week above freezing in February produces tick activity in the same places it produced it in October.

The practical consequence: a winter walk on a bare, mild day is not automatically a zero-risk walk, and a tick found in March is not remarkable enough to doubt.

Fleas move indoors — they do not go away

Winter is when fleas become a house problem rather than a yard problem, and heated homes are the reason. Fleas survive year-round wherever there is an animal to feed on, and indoor development continues in undisturbed, protected places: in carpets, under furniture and along skirting boards.

Two facts explain most winter infestations that seem to appear from nowhere:

• The cocoon resists treatment. The pupal cocoon protects the developing flea from environmental conditions and from insecticides for several days to weeks. A single treatment that appears to work can be followed by a new wave as protected pupae emerge.
• Pupae can wait a very long time. Adult cat fleas may remain quiescent inside the cocoon for up to 30 weeks at around 11 °C and 75% humidity — which is an ordinary unheated porch, basement or spare room.

That is why a flea problem needs a plan measured in weeks, covering the pets and their resting areas together, rather than one application and hope.

The flea life cycle  ·  Clearing an infestation  ·  Spotting flea dirt

The short version, by season

• September to November. Adult tick peak. Keep body checks and pet prevention running. Treat leaf clearing as tick exposure.
• December to February. Tick risk drops with snow cover but returns during thaws. Fleas become the indoor priority; plan treatment over weeks, not days.
• March to April. Ticks resume as soon as the ground clears and temperatures hold above about 4 °C — often before anyone is thinking about it.

Regional timing across North America  ·  Prevention basics  ·  All 36 guides