Does a mild winter mean more insects?

Posted: March 26, 2012 - 15:27 , by ROM
Natural History, Biodiversity, Bugs, Research | Comments () | Comment

Given our warmer-than-average winter this year, ROM entomologists have fielded numerous enquiries about whether mild winter temperatures will result in more bugs this spring and summer. Unfortunately, there is no simple “yes” or “no” answer to this question  — the best response is “It depends”.

There are many variables affecting insect population size: humidity/moisture, habitat suitability and food resources, just to name a few. What may be good for one species is not necessarily good for another. Furthermore, natural variation in population size occurs from year to year in most species.

Early emergences, yes! This year there are many reports of certain insects emerging or becoming active earlier than normal; but seeing insects in March doesn’t necessarily mean that we will be seeing more of them later in the season. Most insects have a limited life span so if they emerge earlier, their flight season will end earlier.

Black fly feeding. Photo by M. Spironello

Black fly feeding. Photo by M. Spironello

Black flies. According to ROM Entomology curator Dr. Doug Currie, the first black flies come out when trees first begin to bud. Winter temperatures have little impact on black fly numbers as most species overwinter as eggs in stream beds.  But if ice break-up occurs earlier than normal, then the season is also likely to begin sooner. Day length also serves as an important cue for emergence of early-season black flies.  In terms of numbers of black flies, the reduced snowpack and lack of rain means that fewer eggs are likely to survive.  So what does this all this mean?  If our current run of warm, dry, weather continues, we will definitely see an earlier than normal emergence of black flies.  On the other hand, there will be fewer adults on the wing, and it’s likely that pest species will disappear well before cottagers begin their late spring or early summer vacations.

Mosquitoes. People are already swatting mosquitoes! Certain species overwinter as adults, which hibernate in protected spaces.  These are the ones that come out earliest in the spring.  However, most Ontario species lay winter-hardy eggs that hatch when conditions are right – typically after snowmelt.  Given that mosquitoes breed in variously-sized pools of standing water, the current lack of snow and dearth of early-season rain means that conditions are less-than ideal for these later emerging populations.  Of course, all of this could change should we experience a period of extended heavy rainfall.  And there’s one more caveat – mosquitoes are on the wing from early spring till late fall; and many species have multiple generations per year.  The upshot is that the current weather only effects the overwintering stages of mosquitoes (and perhaps the first generation or so).  Whatever we predict now, all bets are off later in the season when conditions inevitably change.

Butterflies.  Require flowers to nectar and food plants for their larvae. If they start flying earlier than usual, will there be food for them? The same can happen with queen bees that emerge too early from hibernation, will there be nectar sources?

Eastern Commas overwinter as adults and are one of the first butterflies seen in spring. Photo by A. Guidotti

Eastern Commas overwinter as adults and are one of the first butterflies seen in spring. Photo by A. Guidotti

A possible increase in pests could be balanced by an increase in ‘good’ bugs. Perhaps more wasp (many social wasps are insect predators so they are beneficial) and bee queens survived the winter.  If more of a pest species survived, maybe more of their predators survived as well. It is amazing how nature balances out!

Ticks. The blacklegged deer ticks that carry Lyme disease are found in many places in Ontario. They have a greater survival rate with enhanced moisture conditions in late spring.

Grasshoppers.A warm, dry winter actually enhances the survival of grasshopper eggs. If conditions remain this way, we may see more of them this year.


Grasshopper. Photo by Colin Walton

Grasshopper. Photo by Colin Walton

The early emergences of some species could end up having a negative impact if we suddenly had a cold snap and many of them were killed. It is possible that the newly emerged insect stage isn’t as tolerant to cold temperature as the overwintering stage. Then there would actually be fewer of that species of insect.

A mild winter has no impact on indoor arthropods since temperature is pretty constant indoors year round.

So early emergence doesn’t necessarily mean more insects this spring; there may, in fact, be fewer numbers of certain kinds of insects. On the other hand, insects that are adapted to warmer and drier conditions, like grasshoppers, may thrive this spring and summer.  How things play out depends largely on weather in the coming months.  If you REALLY want to know what the bugs will be like this summer, your best bet is to consult a climatologist!

Read More
Mild winter weather will get bugs buzzing sooner, CBCNews