Ecological survey calendar › Invertebrates
When to survey for invertebrates in Wales and England
Updated November 2026. Based on Natural England's current standing advice and the Environment Agency river sampling method.
Terrestrial invertebrate surveys run from April to September, usually as three to five visits spread across spring, summer and autumn. Aquatic invertebrates in rivers are sampled in spring (March to May) and autumn (September to November).
Survey windows, sensitive periods and works timing
| Activity | Type | When | Notes |
|---|---|---|---|
| Terrestrial invertebrate surveys | Survey | Apr to Sep | Usually three to five visits spread from April to September to cover spring, summer and autumn species. |
| Aquatic invertebrate sampling | Survey | Mar to May; Sep to Nov | Spring (March to May) and autumn (September to November) are the standard river sampling seasons. |
Optimal survey Possible, not ideal Sensitive period Works window
Timing depends on the site, the weather in a given year and what the planning authority and licensing body need. Upland and northern sites can run later. See every species group side by side on the ecological survey calendar.
About invertebrates
Invertebrates make up most of the biodiversity on most sites. Specialist surveys target habitats such as brownfield land, deadwood, wetlands and species-rich grassland.
Legal protection
Some invertebrates are protected under Schedule 5 of the Wildlife and Countryside Act 1981 or the Habitats Regulations, for example marsh fritillary. Many more are species of principal importance.
Licensing
Wales: A licence is needed only for specially protected species.
England: A licence is needed only for specially protected species.
Practical tips
- Plan several visits across spring, summer and autumn, as different groups peak at different times.
- Aquatic samples are taken in standard spring and autumn seasons so results can be compared.
Common questions
When is invertebrate survey season?
April to September for terrestrial invertebrates, with visits spread across the season to catch spring, summer and autumn species (Drake et al., 2007; Natural England standing advice).
When are aquatic invertebrates sampled?
Spring (March to May) and autumn (September to November), the standard seasons for river sampling used by the Environment Agency.
Why can't one visit cover it?
Different invertebrate groups are active at different times of year, so a single visit misses much of the fauna.
Need a survey or advice on timing? Ecoleg's licensed ecologists programme surveys across Wales and England so the right work happens in the right season. Call 07356 123706.
Request a quoteSee the full calendarSources
- Drake, C.M., Lott, D.A., Alexander, K.N.A. and Webb, J. (2007) Surveying terrestrial and freshwater invertebrates for conservation evaluation. Natural England Research Report NERR005.
- Natural England (2025) Protected species and development: advice for local planning authorities, survey timings table (accessed November 2026).
- Environment Agency (2017) Freshwater macro-invertebrate sampling in rivers, operational instruction 018_08.
Updated November 2026. General guidance only: confirm timing for your site with a suitably qualified ecologist.