Massachusetts is home to a wide range of insects and arthropods that shift dramatically with the seasons. From disease-carrying ticks and mosquitoes in summer to overwintering pests that invade homes in fall, knowing what to expect and when can help you avoid bites, protect your property, and recognize genuine threats. The state’s growing season runs roughly from late April through October, with outdoor pest pressure dropping sharply once temperatures fall below about 50°F.
Ticks: The Biggest Health Concern
Ticks are arguably the most important bug to know about in Massachusetts. The blacklegged tick (also called the deer tick) is the primary carrier of Lyme disease, and the state consistently ranks among the highest in the country for tick-borne illness. Beyond Lyme, Massachusetts ticks also transmit anaplasmosis, babesiosis, Borrelia miyamotoi, and Powassan virus. These diseases occur year-round in the state, not just in summer.
Tick activity has two distinct peaks each year. The first begins in March or April and lasts through August. The second arrives in October and November, when adult ticks become active again before winter. The majority of tick-borne disease cases are reported from June through August, which coincides with the nymph stage, when ticks are tiny, hard to spot, and most likely to go unnoticed on your skin.
If you find a tick on yourself, several labs offer identification and pathogen testing. TickReport, based in Amherst, tests for up to 23 diseases and returns results within three business days for $50 to $200. ECO Laboratory in Acton charges $42 to $85 and delivers results in 48 hours. The University of Massachusetts Laboratory of Medical Zoology also publishes anonymized test results through a public surveillance database, which tracks where infected ticks are being found across the state.
Mosquitoes and Virus Season
Mosquito populations in Massachusetts build through late spring and reach peak density from June through September. Two viruses make them more than just a nuisance: Eastern Equine Encephalitis (EEE) and West Nile Virus (WNV). The state conducts seasonal mosquito surveillance from June to October, assigning local risk levels to communities based on testing results.
EEE is rare but extremely dangerous, with a high fatality rate and serious neurological effects in survivors. West Nile is more common but usually causes milder illness, with most infected people showing no symptoms at all. Risk levels vary significantly by town, and the state publishes updated risk maps throughout the season. Areas near freshwater swamps and marshes in southeastern Massachusetts tend to see higher EEE risk.
Greenhead Flies and Other Biters
If you’ve spent time on the North Shore beaches in late July, you’ve met greenhead flies. These large horseflies are a fixture of Essex County’s salt marshes, and the females bite hard to get the blood meal they need for egg development. Their season runs from June to September, with the worst stretch falling in the last two weeks of July through the first week of August.
Greenheads don’t transmit diseases to humans, but their bites are painful and some people develop strong allergic reactions. The flies are such a problem in coastal Essex County that they affect real estate values, beach use, and outdoor recreation. Deer flies, a smaller relative, also bite throughout the summer months, though greenhead populations actually help keep deer fly numbers in check through predation at the larval stage.
Yellowjackets and bald-faced hornets build their colonies to maximum size by late August, which is when sting encounters spike. These wasps become aggressive near food sources and building entrances as colonies grow large and resources become scarce heading into fall.
Invasive Species to Watch For
The spotted lanternfly is the invasive insect getting the most attention in Massachusetts right now. Originally detected in Pennsylvania in 2014, the first breeding population in Massachusetts was confirmed in Fitchburg (Worcester County) in 2021. Since then, established populations have been found in many additional locations across the state.
Spotted lanternflies feed on sap from trees and woody plants. Their primary host is the invasive tree-of-heaven, but they also target grapevines, hops, and fruit trees, making them a serious agricultural concern. They don’t bite or sting people, but heavy infestations weaken plants and leave behind a sticky residue called honeydew that promotes mold growth. If you see one, the state asks that you report it.
Spring Pests: Ants and Termites
Carpenter ants are one of the first insects to become active in spring. Colonies that established themselves the previous year restart expansion from overwintering sites in wall voids, making April through June the period when wood-destroying insect activity is most commonly detected in homes. Unlike termites, carpenter ants don’t eat wood. They excavate it to build nests, leaving behind piles of fine sawdust-like debris.
Subterranean termite swarms in Massachusetts typically occur in April and May, concentrated in eastern coastal counties where soil temperatures warm past 50°F first. Swarming termites look like flying ants with straight antennae and equal-length wings. Termites don’t stop feeding in winter either. They remain active underground and inside wood structures year-round, so damage can accumulate long before anyone notices.
Fall Invaders That Move Indoors
As temperatures drop in September and October, a wave of insects tries to get inside your home. Brown marmorated stink bugs, western conifer seed bugs, Asian lady beetles, and cluster flies are the main culprits. In rural and suburban areas of Massachusetts, susceptible buildings can see hundreds to thousands of these insects penetrating gaps in the building envelope. They’re not dangerous, but they’re a significant nuisance, and stink bugs release a strong odor when crushed or disturbed.
These insects entered your walls in fall but often don’t become visible until winter, when warm days or indoor heating rouse them from hiding. Sealing cracks around windows, doors, and utility penetrations before September is the most effective way to keep them out.
Winter: Fewer Bugs, Not Zero
Outdoor pest activity drops to near zero from December through March for most insects. But indoor infestations continue unchecked. Cockroaches seek warmth and moisture, with January infestations concentrating in kitchens, bathrooms, and basements. Ant colonies can remain active inside heated wall voids, surprising homeowners who associate ants with summer. Bed bugs are entirely temperature-independent indoors and remain active all winter.
The fall invaders mentioned above, especially stink bugs and lady beetles, also show up inside during winter warm spells. They aren’t breeding or feeding in your home. They’re simply waiting out the cold and will leave on their own in spring, though that’s small comfort when they’re clustering on your windows in February.