Success of hand-rearing Common Swift (Apus apus) using a diet based on mealworm (Tenebrio molitor) at a wildlife recovery centre: Analysis of survival and fledgling weights compared to those on previous diets not composed of insects 

Diets for insectivorous birds represent a major challenge. The best diet would be composed of different insect species. This is carried out by some rehabilitation centres currently hand-rearing insectivore species that use mixed insect species (crickets, drones, wax moths larvae, flies), although with a limited number of admissions. A diet based solely on domestic crickets (90%) and large larvae of the wax moth (10%) is used in some rehabilitation centres in Europe specializing in hand-rearing large numbers of swift chicks, with optimal recovery results. However, the crickets produced commercially are extremely expensive.

The results of a comparative study on diets conducted in CRFST (6th European Zoo Nutrition Conference) exposed results posing concerns for the non-insect based diets. On the contrary, the study exhibited excellent results for the diet based only on mealworms, an insect produced commercially which is five times cheaper than the cricket. The mealworm diet is somewhat controversial, as some anecdotal reports attribute health problems to it. Despite this, mealworm is used with success in hand-rearing Chimney swifts (Chaetura pelagica) in the US. Histopathological analysis performed on three swifts fed on mealworms for more than 20 days documented an optimal physical condition and no evidence of disease or organ damage that may be associated with the mealworm diet.

Concerns about the poor results observed in non-insect diets (Rat mince and Kibble cat food) and the results with insect diets led CRFST to make a drastic change in insectivore diet protocols. The mealworm diet has been used in the breeding season 2010 and onwards as a base diet for the hand-rearing of Common Swift, Alpine Swift and other insectivorous birds. The results of the 2010 season with mealworm show a significant increase in the final weights and the values of survival compared to 2009, where the diet was based on Kibble cat food, and over 2008 and prior years where the diet was rat mince. The mealworm diet showed a survival increase of nearly 30 % above the two previous non-insect diets - notably observed in acute clinical categories (72.4 % mealworm diet, 44.0 %  cat food and 45.7 %  rat mince). The euthanasia based on the physical condition at admission was discarded in 2010 (previously acute cases were sacrificed as no improvement was observed under rat mince and cat food, representing around 25 % of the swift admissions). Despite this, after a period in the centre even with the insect diet, around 17 % of chicks were sacrificed due to the irreversible condition of the plumage. Concerning final weights, there was an average increase of 5 grams (adult weights around 40 g) with a remarkable increase of 7 g for the youngest chicks. Importantly, the increases were parallel in all clinical categories, including acute severe cases. Looking at the results, we recommend to discontinue the use of non-insect diets when hand- rearing Common Swifts and a move to a pure insectivorous diet. Mealworm could be a very good alternative when cricket cannot be used for economic reasons. This success is highlighted by the fact that all birds had a high possibility to survive even in extreme condition, We thus discarded any protocol based on poor clinical condition at admission.


Enric Fusté BSc (Hons) MSc MSB



Enric Fusté in Catalonia has been doing revolutionary work on diets for hand-rearing the large numbers of insectivorous bird chicks, especially Common Swifts, found every breeding season in Spain and brought to animal recovery centres.

He has shown that a diet of mealworms can provide optimal results, and it is much cheaper than feeding them crickets. This good news needs to be promulgated as widely as possible as many recovery centres across the world feed these birds with harmful diets, like dog and cat food, which gravely jeopardise their survival.

On 15th January 2012, Enric run the XXIX Sitges Half Marathon near Barcelona to collect money to enable him to present his research work at the 7th EAZA Nutrition Conference (European Association of Zoos and Aquaria) in Zurich.  

The research shows how the mealworm diet increased survival by 30% in comparison with non-insect diets, increasing significantly the final weight and providing optimal plumage and excellent flight performance at release. Even large numbers of extreme cases survived and were released in excellent condition.