Birds

Residents

• Eurasian bittern; in spring, the male's 'booming' song can be heard. Though they are hard to see as they are well camouflaged.
• Common kingfisher present all year and carrying fish back to nests in spring and summer.
• Western marsh harrier; in spring, pairs perform 'sky-dancing' high in the sky.
• Cetti's warbler, the loudest British song bird with a distinctive (once learnt) 'explosive' song.
• Bearded tit,
• Barn owl, they often nest in the woodlands and can be seen hunting at dawn and dusk
• Eurasian bullfinches

Waterfowl include

• Gadwall,
• Great crested grebe and
• Little grebes.

Summer migrants

• Hobby,
• Reed warbler,
• Blackcap,
• Common whitethroat.

Insects

Its Fen provides one of the few breeding sites in Great Britain for the swallowtail. The subspecies found at Strumpshaw, Papilio machaon brittanicus, is endemic to the Fens of Norfolk and Suffolk in the UK.^[3] It is slightly smaller and more heavily marked in black than subspecies machaon and gorganus which are widespread throughout mainland Europe. It nearly always lays its eggs on milk parsley (Peucedanum palustre) in contrast to its European cousin that will select most umbellifers. Swallowtail can be seen from late May to mid-July and often again in mid-August to September. It is the largest resident British butterfly at 8 to 10 cm wingspan.

In early spring and summer the reserve is the habitat of 23 species of dragonfly, including the rare Norfolk hawker which is protected under Schedule 5 of the Wildlife and Countryside Act 1981, and listed in the British Red Data Books on Insects as Category 1 (endangered).

Another important dragon fly is the scarce chaser (Libellula fulva).

Molluscs

• Desmoulin's whorl snail (On the list of endangered species in the British Isles)

Plants

It is one of only a handful of waterbodies in the country to contain holly-leaved naiad (Najas marina), a species on the flowering plant section of the list of endangered species in the British Isles and is protected under Schedule 8 of the Wildlife and Countryside Act 1981. Other important plants are milk parsley, marsh pea, saw sedge, six varieties of orchids including the rare aquatic macrophytes.

Its flower hay meadow is an ecological relict with a high plant diversity due to the continuing centuries old practice of receiving only a cut in late season for a hay crop. In June it is coloured by yellow flag, marsh cinquefoil, bog bean, and ragged robin (a source of nectar for the adult swallowtails). In early July, there are common sorrel, the purple glass Yorkshire fog, southern marsh orchids, yellow rattle and valerian. These are followed by purple loosestrife and meadowsweet.

Mammals

• Eurasian otters
• Water voles
• Chinese water deer

Winter

• Hundreds of ducks, including teals, gadwalls and shovelers gather to feed in the reedbed pools.
• Near dusk, marsh and hen harriers gather to roost.
• On occasional winters, thousands of starlings roost in the reeds attracting sparrowhawks, peregrines and merlins.

Spring

• Courting pairs of marsh harriers perform 'sky-dancing' displays.
• Songs of spring migrant birds including reed and sedge warblers, cuckoos, grasshopper warblers and white throats.
• Swallows and swifts dart across the pools
• Great crested grebes and other waterfowl prepare their nests.
• Lesser spotted and great spotted woodpeckers easily heard drumming in the woodland.
• Booming bitterns can be heard from across the reserve, in 2017, there were up to 3 booming male bitterns on the reserve

Summer

• The UK's largest and one of its rarest butterflies, the swallowtail emerges at this time, remaining on the wing through to July
• Fen meadow rich with flowers including six species of orchids.
• Many butterflies, dragonflies and damselflies including swallowtail butterfly (late May to early July and again in mid-August).
• Hobbies hunt dragonflies.

Autumn

• Ospreys on their southward migration fish.
• Marsh harriers gather in groups to roost.
• Bearded tits form flocks in the reedbeds.