I think the design could be still improved.
We could
- We could make the illustration more colorful. Such as instead only one color; we could choose some other colors in combinations.
Here are some suggestions from web-colors list
$$\begin{array}{c|c|c|c|c}\hline
\textbf{Reds} & \textbf{Yellows} & \textbf{greens}& \textbf{blues}& \textbf{purples}\\\hline
\bbox[red]{\textbf{RED}} & \bbox[Yellow]{\textbf{YELLOW}} & \bbox[limeGreen]{\textbf{LIME-GREEN}}& \bbox[aqua]{\textbf{AQUA}}& \bbox[Fuchsia]{\textbf{FUCHSIA}}\\\hline
\bbox[OrangeRed]{\textbf{ORANGE-RED}} & \bbox[Gold]{\textbf{GOLD}} & \bbox[yellowgreen]{\textbf{YELLOW-GREEN}}& \bbox[DarkTurquoise]{\textbf{DARK-TURQUOISE}}& \bbox[DeepPink]
{\textbf{DEEP-PINK}}\\\hline
\bbox[Tomato]{\textbf{TOMATO}} & \bbox[Goldenrod]{\textbf{GOLDENROD}} & \bbox[OliveDrab]{\textbf{OLIVE-DRAB}}& \bbox[LightSeaGreen]{\textbf{LIHGHT-SEA-GREEN}}& \bbox[MediumVioletRed]{\textbf{MEDIUM-VIOLET-RED}}\\\hline
\bbox[Coral]{\textbf{CORAL}} & \bbox[SandyBrown]{\textbf{SANDY-BROWN}} & \bbox[DarkOliveGreen]{\textbf{DARK-OLIVE-GREEN}}& \bbox[DeepSkyBlue]{\textbf{DEEP-SKY-BLUE}}& \bbox[Purple]{\textbf{PURPLE}}\\\hline
\bbox[Salmon]{\textbf{SALMON}} & \bbox[Peru]{\textbf{PERU}} & \bbox[Olive]{\textbf{OLIVE}}& \bbox[DodgerBlue]{\textbf{DODGER-BLUE}}& \bbox[DarkViolet]{\textbf{DARK-VIOLET}}\\\hline
\bbox[FireBrick]{\textbf{FIREBRICK}} & \bbox[Orange]{\textbf{ORANGE}} & \bbox[ForestGreen]{\textbf{FOREST-GREEN}}& \bbox[CornflowerBlue]{\textbf{CORNFLOWER-BLUE}}& \bbox[Indigo]{\textbf{INDIGO}}\\\hline
\bbox[DarkRed]{\textbf{DARK-RED}} & \bbox[DarkOrange]{\textbf{DARK-ORANGE}} & \bbox[Green]{\textbf{GREEN}}& \bbox[SteelBlue]{\textbf{STEELBLUE}}& \bbox[Pink]{\textbf{PINK}}\\\hline
\bbox[IndianRed]{\textbf{INDIAN-RED}} & \bbox[Moccasin]{\textbf{MOCCASIN}} & \bbox[DarkGreen]{\textbf{DARK-GREEN}}& \bbox[MidnightBlue]{\textbf{MIDNIGHT-BLUE}}& \bbox[RosyBrown]{\textbf{ROSY-BROWN}}\\\hline
\end{array}$$
(The array doesn't indicate any combination, is used to only save the space.)
Here I've shown some samples.
Sample-1: Bright background; only lines colored
Sample-2: Brighter background; shapes fill-coloured
Sample-3: Dark background, Fill-coloured, lines black, bright sharpening.

Sample-4: Dark background, fill-coloured, lines white.

- At the side-space (at left and right side of the text area); we could add some light watermarks.
For this purpose; I would prefer something structural to 'see'; for example the image below:
(Sample originally inspired from an answer by user@WYSIWYG in the question site-design feedback, original photo url)
But not only some arthropods; structures from other animals, plants , fungi , histologic section, TEM/ SEM electron micrograph and chemical-structures too, could be included.