Seasonal Pest Guide

St. Louis Observer

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Missouri  •  Seasonal Pest Guide

Missouri Summer Pest Guide: June, July, and August

Missouri summers are hot, humid, and among the most pest-active months of the year. The heat accelerates insect reproduction cycles, the humidity sustains the moisture conditions that ants, cockroaches, and silverfish require, and the combination of rain events and heat create the standing water and vegetation growth that drives mosquito and wasp populations to their annual peaks. Here is what to expect each month.

Month-by-Month Activity

June — Peak Begins

  • Mosquitoes: Population builds rapidly; evening outdoor activity becomes difficult without barrier treatment or repellent
  • Wasps and yellow jackets: New nests established in spring are now large enough to become a stinging hazard; eave nests, ground nests, and void nests all active
  • Ants: Outdoor foraging peaks; pavement ant and odorous house ant activity highest of the year
  • Ticks: Full summer activity — all three Missouri tick species active
  • Carpenter ants: Foraging workers visible at dusk; established colonies in peak activity

July — Peak Month

  • Mosquitoes: Peak populations — West Nile virus transmission window is open; barrier programs most critical this month
  • Wasps: Yellow jacket and bald-faced hornet nests at maximum size; most aggressive defense behavior
  • Cockroaches: American and German cockroach activity peaks with heat and humidity; most indoor complaint month
  • Fleas: Outdoor flea populations peak in July heat; pets and wildlife activity spreads to yards
  • Spiders: Brown recluse foraging activity highest; greatest indoor encounter frequency

August — Late Summer Pressure

  • Mosquitoes: Still at or near peak; late-season populations can be highest after mid-summer rain events
  • Stinging insects: Yellow jacket colonies largest and most defensive; late-season wasp aggression peaks as colonies sense seasonal end
  • Box elder bugs: Begin appearing on south-facing walls as populations build toward fall aggregation
  • Stink bugs: Adults begin seeking overwintering sites on warm exterior walls; early harbinger of fall invasion pressure
  • Crickets: Field cricket populations peak; begin moving toward structures as August temperatures fluctuate

D&D Pest Control offers summer pest programs for Franklin County and rural Missouri — visit ddpestcontrolmo.com.